complex, and may be divided into two phases, which we may term the A and
the B subcycles. The members of the A cycle are distinguished by the
gelatinous investment being armed with radial spicules, which are absent
from the B form. The close of the A cycle is marked by the large
multinucleate body resolving itself into amoeboid zoospores (3), which
escape from the gelatinous test, and develop into the large multinucleate
adults of the B form. These, like the A form, may reproduce by fission or
budding. At the term of growth, however, they retract their pseudopodia,
expel the excreta, and multiply their nuclei by mitosis (7). Then the body
is resolved into minute 2-flagellate microzoospores (8), which are
_exogamous_ gametes, _i.e._ they will only pair with similar zoospores from
another cyst. The zygote (9-11) resulting from this conjugation is a minute
amoeboid; its nucleus divides repeatedly, a gelatinous test is formed
within which the spicules appear, and so the A form is reconstituted. In
many of the test-bearing forms, whether Lobose or Filose, plastogamic
unions occur, and the two nuclei may remain distinct, leading to
plurinucleate monsters in their offspring by fission, or they may fuse and
form a giant nucleus, a process which has here no relation to normal
syngamy, as it is not associated with any marked change in the alternation
of feeding and fission, etc. In _Trichosphaerium_ also plastogamic unions
between small individuals have for their only result the increase of size,
enabling the produce to deal with {57}larger prey. Temporary encystment in
a "hypnocyst" is not infrequent in both naked and shelled species, and
enables them to tide over drought and other unfavourable conditions.
Schaudinn has discovered and worked out true syngamic processes, some
bisexual, some exogamous, in several other Rhizopods. In _Chlamydophrys
stercorea_ the pairing-cells are equal, and are formed by the aggregation
of the chromidia into minute nuclei around which the greater part of the
cytoplasm aggregates, while the old nucleus (with a little cytoplasm) is
lost. These brood-cells are 2-flagellate pairing-cells, which are
exogamous: the zygote is a brown cyst; if this be swallowed by a mammal,
the original _Chlamydophrys_ appears in its faeces.[72]
_Centropyxis aculeata_, a species very common in mud or moss, allied to
_Difflugia_, also forms a brood by aggregation around nuclei derived from
chromidia. The brood-cells are amoeboid, and secrete hemispherical shells
like those of _Arcella_; some first divide into four smaller ones, before
secreting the shell. Pairing takes place between the large and the small
forms; and the zygote encysts. Weeks or months afterwards the cyst opens
and its contents creep out as a minute _Centropyxis_. Finally, _Amoeba
coli_ produces its zygote in a way recalling that of _Actinosphaerium_ (pp.
73-75, Fig. 21): the cell encysts; its nucleus divides, and each daughter
divides again into two, which fuse reciprocally. Thus the cyst contains two
zygote nuclei. After a time each of these divides twice, so that the mature
cyst contains eight nuclei. Probably when swallowed by another animal they
liberate a brood of eight young amoebae. Thus in different members of this
group we have exogamy, both equal and bisexual, and endogamy.
Most of the Rhizopoda live among filamentous Algae in pools, ponds, and in
shallow seas, etc.; some are "sapropelic" or mud-dwellers (many species of
_Amoeba_, _Pelomyxa_, _Difflugia_, etc.), others frequent the roots of
mosses. _Amoeba coli_ is often found as a harmless denizen of the large
intestine of man. _Amoeba histolytica_, lately distinguished therefrom by
Schaudinn, is the cause of tropical dysentery. It multiplies enormously in
the gut, and is found extending into the tissues, and making its way into
the abscesses that so frequently supervene in the liver and other organs.
_Chlamydophrys stercorea_ is found in the {58}faeces of several mammals.
The best monograph of this group is that of Penard.[73]
2. FORAMINIFERA[74]
_Sarcodina with no central capsule or distinction of ectosarc; the
pseudopodia fine, branching freely, and fusing where they meet to form
protoplasmic networks, or the outermost in the pelagic forms radiating, but
without a central or axial filament: sometimes dimorphic, reproducing by
fission and by rhizopod or flagellate germs in the few cases thoroughly
investigated: all marine (with the exception of some of the
Allogromidiaceae), and usually provided with a test of carbonate of lime
("vitreous" calcite, or "porcellanous" aragonite?), or of cemented
particles of sand ("arenaceous"); test-wall continuous, or with the walls
perforated by minute pores or interstices for the protrusion of
pseudopodia._
The classification of Carpenter (into _Vitreous_ or _Perforate_,
_Porcellanous_ or _Imperforate_, and _Arenaceous_), according to the
structure of the shell, had proved too artificial to be used by Brady in
the great Monograph of the Foraminifera collected by the "Challenger"
Expedition,[75] and has been modified by him and others since then. We
reproduce Lister's account of Brady's classification.[76] We must, however,
warn the tyro that its characterisations are not definitions (a feature of
all other recent systems), for rigid definitions are impossible: here as in
the case, for instance, of many Natural Orders of Plants, transitional
forms making the establishment of absolute boundaries out of the question.
In the following classification we do not think it, therefore, necessary to
complete the characterisations by noting the extremes of variation within
the orders:—
1. Allogromidiaceae: simple forms, often fresh-water and similar to
Rhizopoda; test 0, or chitinous, gelatinous, or formed of cemented
particles, whether secreted platelets or ingested granules. _Biomyxa_,
Leidy = _Gymnophrys_, Cienk.; {59}_Diaphorodon_, Archer; _Allogromia_,
Rhumbl. (= _Gromia_, auctt.[77] nec Duj.) (Fig. 14, 1); _Lieberkühnia_,
Cl. and Lachm. (Fig. 12); _Microgromia_, R. Hertw. (Fig. 11);
_Pamphagus_, Bailey.
2. Astrorhizidaceae: test arenaceous, often large, never truly chambered,
or if so, asymmetrical. _Astrorhiza_, Sandahl; _Haliphysema_, Bowerb.;
_Saccammina_, M. Sars (Fig. 13, 1); _Loftusia_, Brady.
3. Lituolidaceae: test arenaceous, often symmetrical or regularly spiral,
isomorphous with calcareous forms: the chambers when old often
"labyrinthine" by the ingrowth of wall-material. _Lituola_, Lam.;
_Reophax_, Montf.; _Ammodiscus_, Reuss; _Trochammina_, Parker and
Jeffreys.
4. Miliolidaceae: test porcellanous, imperforate, spirally coiled or
cyclic, often chambered except in _Cornuspira_: simple in _Squamulina_.
_Cornuspira_, Max Sch.; _Peneroplis_, Montf.; _Miliolina_, Lam. (incl.
_Biloculina_ (Fig. 15), _Triloculina_, _Quinqueloculina_ (Figs. 14, 4;
15, B), _Spiroloculina_ (Fig. 13, 5) of d'Orb.); _Alveolina_, d'Orb.;
_Hauerina_, d'Orb.; _Calcituba_, Roboz; _Orbitolites_, Lam.;
_Orbiculina_, Lam.; _Alveolina_, Park. and Jeffr.; _Nubecularia_, Def.;
Squamulina, Max Sch. (Fig. 14, 3).
5. Textulariaceae: test calcareous, hyaline, perforated; chambers
increasing in size in two alternating rows, or three, or passing into a
spiral. _Textularia_, Def.; _Bulimina_, d'Orb.; _Cassidulina_, d'Orb.
6. Cheilostomellaceae: test vitreous, delicate, finely perforated,
chambered, isomorphic with the spiral forms of the Miliolidaceae.
_Cheilostomella_, Reuss.
7. Lagenaceae: Test vitreous, very finely perforate, chambers with a
distinct pylome projecting (ectosolenial), or turned in (entosolenial),
often succeeding to form a necklace-like shell. _Lagena_, Walker and Boys
(Fig. 13, 2); _Nodosaria_, Lam. (Fig. 13, 3); _Cristellaria_, Lam.;
_Frondicularia_, Def. (Fig. 13, 4); _Polymorphina_, Lam.; _Ramulina_,
Wright.
8. Globigerinidae: test vitreous, perforate; chambers few, dilated, and
arranged in a flat or conical spiral, usually with a crescentic pylome to
the last. _Globigerina_, d'Orb. (Figs. 13, 6; 16, 2); _Hastigerina_, Wyv.
Thoms.; _Orbulina_, d'Orb. (Fig. 16, 1).
9. Rotaliaceae; test vitreous, perforate, usually a conical spiral (like
a snail), chambers often subdivided into chamberlets, and with a proper
wall, and intermediate skeleton traversed by canals. _Rotalia_, Lam.
(Fig. 14, 2); _Planorbulina_, d'Orb. (Fig. 13, 9); _Polytrema_, Risso;
_Spirillina_, Ehr. (non-septate); _Patellina_, Will.; _Discorbina_, P.
and J. (Fig. 13, 7).
10. Nummulitaceae: test usually a complex spiral, the turns completely
investing their predecessors: wall finely tubular, often with a proper
wall and intermediate skeleton. _Fusulina_, Fisch.; _Polystomella_, Lam.;
_Nummulites_, d'Orb. (Fig. 13, 11); _Orbitoides_, d'Orb.
The Allogromidiaceae are a well-marked and distinct order, on the whole
resembling the Rhizopoda Filosa, and are often found with them in fresh
water, while all other Foraminifera are marine. The type genus,
_Allogromia_ (Fig. 14, 1), has an oval chitinous shell. _Microgromia
socialis_ (Fig. 11) is often found in aggregates, the pseudopodia of
neighbours fusing where they meet into a {60}common network. This is due to
the fact that one of the two daughter-cells at each fission, that does not
retain the parent shell, remains in connexion with its sister that does:
sometimes, however, it retracts its pseudopodia, except two which become
flagella, wherewith it can swim off. The test of _Pamphagus_ is a mere
pellicle. In _Lieberkühnia_ (Fig. 12) it is hardly that; though the body
does not give off the fine pseudopodia directly, but emits a thick process
or "stylopodium"[78] comparable to the protoplasm protruded through the
pylome of its better protected allies; and from this, which often stretches
back parallel to the elongated body, the reticulum of pseudopodia is
emitted. _Diaphorodon_ has a shell recalling that of _Difflugia_ (Fig. 10,
D, p. 55), formed of sandy fragments, but with interstices between them
through which as well as through the two pylomes the pseudopodia pass. In
all of these the shell is formed as in the Rhizopods once for all, and does
not grow afterwards; and the fresh-water forms, which are the majority,
have one or more contractile vacuoles; in _Allogromia_ they are very
numerous, scattered on the expanded protoplasmic network.
[Illustration: FIG. 11.—_Microgromia socialis._ A, entire colony; B, single
zooid; C, zooid which has undergone binary fission, with one of the
daughter-cells creeping out of the shell; D, flagellula. _c.vac_,
Contractile vacuole; _nu_, nucleus; _sh_, shell. (From Parker and Haswell,
after Hertwig and Lesser.)]
{61}[Illustration: FIG. 12.—_Lieberkühnia_, a fresh-water Rhizopod, from
the egg-shaped shell of which branched pseudopodial filaments protrude.
(From Verworn.)]
The remaining marine families may all be treated of generally, before
noting their special characters. Their marine habitat is variable, but in
most cases restricted. A few extend up the brackish water of estuaries: a
large number are found between tide-marks, or on the so-called littoral
shelf extending to deep water; they are for the most part adherent to
seaweeds, or lie among sand or on the mud. Other forms, again, are pelagic,
such as _Globigerina_ (Figs. 13, 6, 16, 17) and its allies, and float as
part of the plankton, having the surface of their shells extended by
delicate spines, their pseudopodia long and radiating, and the outer part
of their cytoplasm richly vacuolated ("alveolate"), and probably containing
a liquid lighter than sea water, as in the Radiolaria. Even these, after
their death and the decay of the protoplasm, must sink to the bottom
(losing the fine spines by solution as they fall); and they accumulate
there, to form a light oozy mud, the "Globigerina-ooze" of geographers, at
depths where the carbonic acid under pressure is not adequate to dissolve
the more solid calcareous matter. Grey Chalk is such an ooze, consolidated
by {62}the lapse of time and the pressure of superincumbent layers. Some
Foraminifera live on the sea bottom even at the greatest depths, and of
course their shell is not composed of calcareous matter. Foraminifera may
be obtained for examination by carefully washing sand or mud, collected on
the beach at different levels between tide-marks, or from dredgings, or by
carefully searching the surface of seaweeds, or by washing their roots, or,
again, by the surface or deep-sea tow-net. The sand used to weight sponges
for sale is the ready source of a large number of forms, and may be
obtained for the asking from the sponge-dealers to whom it is a useless
waste product. If this sand is dried in an oven, and then poured into
water, the empty shells, filled with air, will float to the surface, and
may be sorted by fine silk or wire gauze.
From the resemblance of the shells of many of them to the Nautilus they
were at first described as minute Cephalopods, or Cuttlefish, by
d'Orbigny,[79] and their true nature was only elucidated in the last
century by the labours of Williamson, Carpenter, Dujardin, and Max
Schultze. At first they possess only one nucleus, but in the adult stage
may become plurinucleate without dividing, and this is especially the case
in the "microsphaeric" states exhibited by many of those with a complex
shell; the nucleus is apt to give off fragments (chromidia) which lie
scattered in the cytoplasm. At first, too, in all cases, the shell has but
a single chamber, a state that persists through life in some. When the
number of chambers increases, their number has no relation to that of the
nuclei, which remains much smaller till brood-formation sets in.
The shell-substance, if calcareous, has one of the two types, porcellanous
or vitreous, that we have already mentioned, but _Polytrema_, a form of
very irregular shape, though freely perforated, is of a lovely pink colour.
In the calcareous shells sandy particles may be intercalated, forming a
transition to the Arenacea. In these the cement has an organic base
associated with calcareous or ferruginous matter; in some, however, the
cement is a phosphate of iron. The porcellanous shells are often deep brown
by transmitted light.
{63}[Illustration: FIG. 13.—Shells of _Foraminifera_. In 3, 4, and 5, _a_
shows the surface view, and _b_ a section; 8_a_ is a diagram of a coiled
cell without supplemental skeleton; 8_b_ of a similar form with
supplemental skeleton (_s.sk_); and 10 of a form with overlapping whorls;
in 11_a_ half the shell is shown in horizontal section; _b_ is a vertical
section; _a_, aperture of the shell; 1-15, successive chambers, 1 being
always the oldest or initial chamber. (From Parker and Haswell, after other
authors.)]
Despite the apparent uniformity of the protoplasmic body in this group, the
shell is infinitely varied in form. As Carpenter writes, in reference to
the Arenacea, "There is nothing more wonderful in nature than the building
up of these elaborate and symmetrical structures by mere jelly-specks,
presenting no traces {64}whatever of that definite organisation which we
are accustomed to regard as necessary to the manifestations of conscious
life.... The tests (shells) they construct when highly magnified bear
comparison with the most skilful masonry of man. From the same sandy bottom
one species picks up the coarsest quartz grains, unites them together with
a ferruginous cement, and thus constructs a flask-shaped test, having a
short neck and a single large orifice; another picks up the finer grains
and puts them together with the same cement into perfectly spherical tests
of the most extraordinary finish, perforated with numerous small pores
disposed at pretty regular intervals. Another species selects the minutest
sand grains and the terminal portions of sponge-spicules, and works them up
together—apparently with no cement at all, but by the mere laying of the
spicules—into perfect white spheres like homoeopathic globules, each
showing a single-fissured orifice. And another, which makes a straight,
many-chambered test, the conical mouth of each chamber projecting into the
cavity of the next, while forming the walls of its chambers of ordinary
sand grains rather loosely held together, shapes the conical mouths of the
chambers by firmly cementing together the quartz grains which border it."
The structure of the shell is indeed variable. The pylome may be single or
represented by a row of holes (_Peneroplis_, _Orbitolites_), or, again,
there may be several pylomes (_Calcituba_); and, again, there are in
addition numerous scattered pores for the protrusion of pseudopodia
elsewhere than from the stylopodium, in the whole of the "Vitrea" and in
many "Arenacea"; and, as we shall see, this may exercise a marked influence
on the structure of the shell.
In some cases the shell is simple, and in _Cornuspira_ and _Spirillina_
increases so as to have the form of a flat coiled tube. In _Calcituba_ the
shell branches irregularly in a dichotomous way, and the older parts break
away as the seaweed on which they grow is eaten away, and fall to the
bottom, while the younger branches go on growing and branching. The fallen
pieces, if they light on living weed, attach themselves thereto and repeat
the original growth; if not, the protoplasm crawls out and finds a fresh
weed and forms a new tube. In the "Polythalamia" new chambers are formed by
the excess of the protoplasm emerging and surrounding itself with a shell,
organically united with the existing chamber or chambers, and in a
space-relation which follows definite laws characteristic of the species or
of its stage of growth, so as to give rise to circular, spiral, or
irregular complexes (see Fig. 13).
{65}[Illustration: FIG. 14.—Various forms of _Foraminifera_. In 4,
_Miliola_, _a_, shows the living animal; _b_, the same killed and stained;
_a_, aperture of shell; _f_, food particles; _nu_, nucleus; _sh_, shell.
(From Parker and Haswell, after other authors.)]
In most {66}cases the part of the previously existing chamber next the
pylome serves as the hinder part of the new chamber, and the old pylome
becomes the pore of communication. But in some of the "Perforata" each new
chamber forms a complete wall of its own ("proper wall," Fig. 13, 8_b_),
and the space between the two adjacent walls is filled with an intermediate
layer traversed by canals communicating with the cavities of the chambers
("intermediate skeleton"), while an external layer of the same character
may form a continuous covering. The shell of the Perforata may be adorned
with pittings or fine spines, which serve to increase the surface of
support in such floating forms as _Globigerina_, _Hastigerina_, and the
like (Fig. 17). In the "Imperforata" the outer layer is often ornamented
with regular patterns of pits, prominences, etc., which are probably formed
by a thin reflected external layer of protoplasm. In some of the "Arenacea"
a "labyrinthine" complex of laminae is formed.
A very remarkable point which has led to great confusion in the study of
the Foraminifera, is the fact that the shell on which we base our
characters of classification, may vary very much, even within the same
individual. Thus in the genus _Orbitolites_ the first few chambers of the
shell have the character of a Milioline, in _Orbiculina_ of a _Peneroplis_.
The arrangements of the Milioline shell, known as Triloculine,
Quinqueloculine, and Biloculine respectively, may succeed one another in
the same shell (Figs. 14 4, 15). A shell may begin as a spiral and end by a
straight continuation: again, the spherical _Orbulina_ (Fig. 16 1) is
formed as an investment to a shell indistinguishable from _Globigerina_,
which is ultimately absorbed. In some cases, as Rhumbler has pointed out,
the more recent and higher development shows itself in the first formed
chambers, while the later, younger chambers remain at a lowlier stage, as
in the case of the spiral passing into a straight succession; but the other
cases we have cited show that this is not always the case. In _Lagena_
(Fig. 13 2) the pylome is produced into a short tube, which may protrude
from the shell or be turned into it, so that for the latter form the genus
_Entosolenia_ was founded. Shells identical in minute sculpture are,
however, found with either form of neck, and, moreover, the polythalamial
shells (_Nodosaria_, Fig. 13 3), formed of a nearly straight succession of
_Lagena_-like chambers, may have these chambers with their
{67}communications on either type. Rhumbler goes so far as to suggest that
all so-called _Lagena_ shells are either the first formed chamber of a
_Nodosaria_ which has not yet become polythalamian by the formation of
younger ones, or are produced by the separation of an adult _Nodosaria_
into separate chambers.
[Illustration: FIG. 15.—A, Megalospheric; B, microspheric shell of
_Biloculina_. _c_, The initial chamber. The microspheric form begins on the
_Quinqueloculina_ type. (From Calkins' _Protozoa_.)]
Many of the chambered species show a remarkable dimorphism, first noted by
Schlumberger, and finally elucidated by J. J. Lister and Schaudinn. It
reveals itself in the size of the initial chamber; accordingly, the two
forms may be distinguished as "microspheric" and "megalospheric"
respectively (Fig. 15), the latter being much the commoner. The
microspheric form has always a plurality of nuclei, the megalospheric a
single one, except at the approach of reproduction. Chromidial masses are,
however, present in both forms. The life-history has been fully worked out
in _Polystomella_ by Schaudinn, and in great part in _Polystomella_,
_Orbitolites_, etc., by Lister; and the same scheme appears to be general
in the class, at least where the dimorphism noted occurs. The microspheric
form gives birth only to the megalospheric, but the latter may reproduce
megalospheric broods, or give rise to swarmers, which by their (exogamous)
{68}conjugation produce the microspheric young. The microspheric forms
early become multinucleate, and have also numerous chromidia detached from
the nuclei, which they ultimately replace. These collect in the outer part
of the shell and aggregate into new nuclei, around which the cytoplasm
concentrates, to separate into as many amoeboid young "pseudopodiospores"
as there are nuclei. These escape from the shell or are liberated by its
disintegration, and invest themselves with a shell to form the initial
large central chamber or megalosphere.
[Illustration: FIG. 16.—1, _Orbulina universa_. Highly magnified. 2,
_Globigerina bulloides_. Highly magnified. (From Wyville Thomson, after
d'Orbigny.)]
In the ordinary life of the megalospheric form the greater part of the
chromatic matter is aggregated into a nucleus, some still remaining
diffused. At the end of growth the nucleus itself disintegrates, and the
chromidia concentrate into a number of small vesicular nuclei, each of
which appropriates to itself a small surrounding zone of thick plasm and
then divides by mitosis twice; and the 4-nucleate cells so formed are
resolved into as many 1-nucleate, 2-flagellate swarmers, which conjugate
{69}only _exogamously_.[80] The fusion of their nuclei takes place after
some delay: ultimately the zygote nucleus divides into two, a shell is
formed, and we have the microsphere, which is thus pluri-nucleate _ab
initio_. As we have seen, the nuclei of the microsphere are ultimately
replaced by chromidia, and the whole plasmic body divides into
pseudopodiospores, which grow into the megalospheric form.
[Illustration: FIG. 17.—Shell of _Globigerina bulloides_, from tow-net,
showing investment of spines. (From Wyville Thomson.)]
In the Perforate genera, _Patellina_ and _Discorbina_, plastogamy precedes
brood formation, the cytoplasms of the 2-5 pairing individuals contracting
a close union; and then the nuclei proceed to break up _without fusion_,
while the cytoplasm aggregates around the young nuclei to form amoebulae,
which acquire a shell and separate. In both cases it is the forms with a
single nucleus, corresponding to _megalospheric_ forms that so pair, and
the brood-formation is, _mutatis mutandis_, the same as in these forms.
Similar individuals may reproduce in the same way, in both genera, without
this plastogamic pairing, which is therefore, though probably advantageous,
not essential. If pseudopodiospores form their shells while near one
another, they may coalesce to form monsters, as often happens in
_Orbitolites_.[81]
The direct economic uses of the Foraminifera are perhaps greater than those
of any other group of Protozoa. The Chalk is {70}composed largely of
_Textularia_ and allied forms, mixed with the skeletons of
Coccolithophoridae (pp. 113-114), known as Coccoliths, etc. The Calcaire
Grossier of Paris, used as a building stone, is mainly composed of the
shells of Miliolines of Eocene age; the Nummulites of the same age of the
Mediterranean basin are the chief constituent of the stone of which the
Pyramids of Egypt are built. Our own Oolitic limestones are composed of
concretions around a central nucleus, which is often found to be a minute
Foraminiferous shell.
The palaeontology of the individual genera is treated of in Chapman's and
Lister's recent works. They range from the Lower Cambrian characterised by
perforated hyaline genera, such as _Lagena_, to the present day. Gigantic
arenaceous forms, such as _Loftusia_, are among the Tertiary
representatives; but the limestones formed _principally_ of their shells
commence at the Carboniferous. The so-called Greensands contain greenish
granules of "glauconite," containing a ferrous silicate, deposited as a
cast in the chambers of Foraminifera, and often left exposed by the
solution of the calcareous shell itself. Such granules occur in deep-sea
deposits of the present day.[82]
3. HELIOZOA
_Sarcodina with radiate non-anastomosing pseudopodia of granular
protoplasm, each with a stiff axial rod passing into the body plasma; no
central capsule, nor clear ectoplasm; skeleton when present siliceous;
nucleus single or multiple; contractile vacuole (or vacuoles) in
fresh-water species, superficial and prominent at the surface in diastole;
reproduction by fission or budding in the active condition, or by
brood-formation in a cyst, giving rise to resting spores; conjugation
isogamous in the only two species fully studied; habitat floating or among
weeds, mostly fresh water._
1. Naked or with an investment only when encysted.
APHROTHORACA.—_Actinolophus_ F.E. Sch.; _Myxastrum_ Haeck.;
_Gymnosphaera_ Sassaki; _Dimorpha_ (Fig. 37, 5, p. 112) Gruber;
_Actinomonas_ Kent; _Actinophrys_ Ehrb.; _Actinosphaerium_ St.;
_Camptonema_ Schaud; _Nuclearia_ Cienk.
{71}2. Invested with a gelatinous layer, sometimes traversed by a firmer
elastic network.
CHLAMYDOPHORA.—_Heterophrys_ Arch.; _Mastigophrys_ Frenzel;
_Acanthocystis_, Carter.
3. Ectoplasm with distinct siliceous spicules.
CHALAROTHORACA.—_Raphidiophrys_ Arch.
4. Skeleton a continuous, fenestrated shell, sometimes stalked.
DESMOTHORACA.—_Myriophrys_ Penard; _Clathrulina_ Cienk.; _Orbulinella_
Entz.
This class were at first regarded and described as fresh-water Radiolaria,
but the differences were too great to escape the greatest living specialist
in this latter group, Ernst Haeckel, who in 1866 created the Heliozoa for
their reception. We owe our knowledge of it mainly to the labours of
Cienkowsky, the late William Archer, F. E. Schulze, R. Hertwig, Lesser, and
latterly to Schaudinn, who has monographed it for the "Tierreich" (1896);
and Penard has published a more recent account.
[Illustration: FIG. 18.—_Actinophrys sol._ _a_, Axial filament of
pseudopod; _c.v_, contractile vacuole; _n_, nucleus. (From Lang's
_Comparative Anatomy_, after Grenacher.)]
_Actinophrys sol_ Ehrb. (Fig. 18) is a good and common type. It owes its
name to its resemblance to a conventional drawing of the sun, with a
spherical body and numerous close-set diverging rays. The cytoplasm shows a
more coarsely vacuolated outer layer, sometimes called the ectosarc, and a
denser internal layer the endosarc. In the centre of the figure is the
large nucleus, to which the continuations of the rays may be seen to
converge; the pseudopodia contain each a stiffish axial filament,[83] which
is covered by the fine granular plasm, showing currents of the granules.
The axial filament disappears when the pseudopodia are retracted or bent,
and is regenerated afterwards. This bending occurs when a living prey
touches and adheres to a ray, all its neighbours bending in like the
tentacles of a Sundew. The prey is carried down to the surface of the
ectoplasm, and {72}sinks into it with a little water, to form a nutritive
vacuole. Fission is the commonest mode of reproduction, and temporary
plastogamic unions are not uncommon. Arising from these true conjugations
occur, two and two, as described by Schaudinn. A gelatinous cyst wall forms
about the two which are scarcely more than in contact with their rays
withdrawn. Then in each the nucleus divides into two, one of which passes
to the surface, and is lost (as a "polar body"), while the other approaches
the corresponding nucleus of the mate, and unites with it, while at the
same time the cytoplasms fuse. Within the gelatinous cyst the zygote so
formed divides to produce two sister resting spores, from each of which,
after a few days, a young _Actinophrys_ escapes, as may take place indeed
after encystment of an ordinary form without conjugation.
[Illustration: FIG. 19.—_Actinosphaerium eichornii._ A, entire animal with
two contractile vacuoles (_c.vac_); B, a portion much magnified, showing
alveolate cytoplasm, pseudopodia with axial rods, non-nucleate cortex
(_cort_), multiple nuclei (_nu_) of endoplasm (_med_), and food-vacuole
(_chr_). (From Parker and Haswell.)]
The axial rods of the pseudopodia may pass either to the circumference of
the nucleus or to a central granule, corresponding, it would appear, to a
centrosome or blepharoplast; or again, {73}in the plurinucleate marine
genus _Camptonema_, each rod abuts on a separate cap on the outer side of
each nucleus. The nucleus is single in all but the genera
_Actinosphaerium_, _Myxastrum_, _Camptonema_, and _Gymnosphaera_. The
movements of this group are very slow, and are not well understood. A slow
rolling over on the points of the rays has been noted, and in _Camptonema_
they move very decidedly to effect locomotion, the whole body also moving
Amoeba-fashion; but of the distinct movements of the species when floating
no explanation can be given. The richly vacuolate ectoplasm undoubtedly
helps to sustain the cell, and the extended rays must subserve the same
purpose by so widely extending the surface. _Dimorpha_ (Fig. 37, 5, p. 112)
has the power of swimming by protruding a pair of long flagella from the
neighbourhood of the eccentric nucleus; and _Myriophrys_ has an investment
of long flagelliform cilia. _Actinomonas_ has a stalk and a single
flagellum in addition to the pseudopodia; these genera form a transition to
the Flagellata.
Several species habitually contain green bodies, which multiply by
bipartition, and are probably Zoochlorellae, Chlamydomonadidae of the same
nature as we shall find in certain Ciliata (pp. 154, 158) in fresh-water
Sponges (see p. 175), in _Hydra viridis_ (p. 256), and the marine
Turbellarian _Convoluta_ (Vol. II. p. 43).
Reproduction by fission is not rare, and in some cases (_Acanthocystis_)
the cell becomes multinuclear, and buds off 1-nucleate cells. In such cases
the buds at first lack a centrosome, and a new one is formed first in the
nucleus, and passes out into the cytoplasm. These buds become 2-flagellate
before settling down. In _Clathrulina_ the formation of 2-flagellate
zoospores has long been known (Fig. 20, 3). In _Actinosphaerium_ (Figs. 19,
21), a large species, differing from _Actinophrys_ only in the presence of
numerous nuclei in its endoplasm, a peculiar process, which we have
characterised as _endogamy_, results in the formation of resting spores.
The animal retracts its rays and encysts; and the number of nuclei is much
reduced by their mutual fusion, or by the solution of many of them, or by a
combination of the two processes. The body then breaks up into cells with a
single nucleus, and each of these surrounds itself with a wall to form a
cyst of the second order.
{74}[Illustration: FIG. 20.—Various forms of Heliozoa. In 3, _a_ is the
entire animal and _b_ the flagellula; _c.vac_, contractile vacuole; _g_,
gelatinous investment; _nu_, nucleus; _psd_, pseudopodia; _sk_, siliceous
skeleton; _sp_, spicules. (From Parker and Haswell, after other authors.)]
Each of these divides, and the two sister cells then conjugate after the
same fashion as in _Actinophrys_, but the nuclear divisions to form the
coupling nucleus are two in number, _i.e._ the nucleus divides into two,
one of which goes to the surface as the first polar body, and the sister of
this again divides to form a second polar body (which also passes to
{75}the surface) and a pairing nucleus.[84] The two cells then fuse
completely, and surround themselves with a second gelatinous cyst wall,
separated from the outer one by a layer of siliceous spicules. The nucleus
appears to divide at least twice before the young creep out, to divide
immediately into as many _Actinophrys_-like cells as there were nuclei;
then each of these multiplies its nuclei, to become apocytial like the
adult form.
[Illustration: FIG. 21.—Diagram illustrating the conjugation of
_Actinosphaerium_. 1, Original cell; 2, nucleus divides to form two,
N_{2}N_{2}; 3, each nucleus again divides to form two, N_{3} and _n__{3},
the latter passing out with a little cytoplasm as an abortive cell; 4,
repetition of the same process as in 3; 5, the two nuclei N_{4} have fused
in syngamy to form the zygote nucleus N_{z}.]
Schaudinn admits 24 genera (and 7 doubtful) and 41 species (and 18
doubtful). None are known fossil. Their geographical distribution is
cosmopolitan, as is the case with most of the minute fresh-water Protista;
8 genera are exclusively marine, and _Orbulinella_ has only been found in a
salt-pond; _Actinophrys sol_ is both fresh-water and marine, and
_Actinolophus_ has 1 species fresh-water, the other marine. One of the 14
species of _Acanthocystis_ is marine; the remaining genera and species are
all inhabitants of fresh water.[85]
4. RADIOLARIA
_Sarcodina with the protoplasm divided by a perforated chitinous central
capsule into a central mass surrounding the nucleus, and an outer layer;
the pseudopodia radiate, never anastomosing enough to form a marked
network; skeleton either siliceous, of spicules, or perforated; or of
definitely arranged spicules of proteid matter (acanthin), sometimes also
coalescing into a latticed shell; reproduction by fission and by zoospores
formed in the central capsule. Habitat marine, suspended at the surface
(plankton), at varying depths (zonarial), or near the bottom (abyssal)._
{76}[Illustration: FIG. 22.—_Collozoum inerme._ A, B, C, three forms of
colony; D, small colony with central capsules (_c.caps_), containing
nuclei, and alveoli (_vac_) in ectoplasm; E, isospores, with crystals
(_c_); F, anisospores; _nu_, nucleus. (From Parker and Haswell.)]
The following is Haeckel's classification of the Radiolaria:—
I. PORULOSA (HOLOTRYPASTA).—Homaxonic, or nearly so. Central capsule
spherical in the first instance; pores numerous, minute, scattered;
mostly pelagic.
A. SPUMELLARIA (PERIPYLAEA).—Pores evenly scattered; skeleton of solid
siliceous spicules, or continuous, and reticulate or latticed, rarely
absent; nucleus dividing late, as an antecedent to reproduction.
B. ACANTHARIA (ACTIPYLAEA).—Pores aggregated into distinct areas;
skeleton of usually 20 centrogenous, regularly radiating spines of
acanthin, whose branches may coalesce into a latticed shell; nucleus
dividing early.
II. OSCULOSA (MONOTRYPASTA).—Monaxonic; pores of central capsule limited
to the basal area (osculum), sometimes accompanied by two (or more)
smaller oscula at apical pole, mostly zonarial or abyssal.
C. NASSELLARIA (MONOPYLAEA).—Central capsule ovoid, of a single layer;
pores numerous on the operculum or basal field; skeleton siliceous,
usually with a principal tripod or calthrop-shaped spicule passing, by
branching, into a complex ring or a latticed bell-shaped shell; nucleus
eccentric, near apical pole.
D. PHAEODARIA (CANNOPYLAEA, Haeck.; TRIPYLAEA, Hertw.).—Central capsule
spheroidal, of two layers, in its outer layer an operculum, with
radiate ribs and a single aperture, beyond which protrudes the outer
layer; osculum basal, a dependent tube (proboscis); accessory oscula,
when present, simpler, usually two placed symmetrically about the
apical pole; skeleton siliceous, with a combination of organic matter,
often of hollow spicules; nucleus sphaeroidal, eccentric; extracapsular
protoplasm containing an accumulation of dusky pigment granules
("phaeodium").
{77}[Illustration: FIG. 23.—_Actinomma asteracanthion._ A, the shell with
portions of the two outer spheres broken away; B, section showing the
relations of the skeleton to the animal, _cent.caps_, Central capsule;
_ex.caps.pr_, extra-capsular protoplasm: _nu_, nucleus; _sk._1, outer,
_sk._2, middle, _sk._3, inner sphere of skeleton. (From Parker and Haswell,
after Haeckel and Hertwig.)]
A. SPUMELLARIA.
Sublegion (1). COLLODARIA.[86]—Skeleton absent or of detached spicules;
colonial or simple.
Order i. COLLOIDEA.—Skeleton absent. (Families 1, 2.) _Thalassicolla_
Huxl.; _Thalassophysa_ Haeck.; _Collozoum_ Haeck.; _Collosphaera_ J.
Müll.; _Actissa_ Haeck.
Order ii. BELOIDEA.—Skeleton spicular. (Families 3, 4.)
Sublegion (2). SPHAERELLARIA.—Skeleton continuous, latticed or spongy,
reticulate.
Order iii. SPHAEROIDEA.—Skeleton of one or several concentric spherical
shells; sometimes colonial. (Families 5-10.) _Haliomma_ Ehrb.;
_Actinomma_ Haeck. (Fig. 23).
Order iv. PRUNOIDEA.—Skeleton a prolate sphaeroid or cylinder,
sometimes constricted towards the middle, single or concentric.
(Families 11-17.)
Order v. DISCOIDEA.—Shell flattened, of circular plan, simple or
concentric, rarely spiral. (Families 18-23.)
Order vi. LARCOIDEA.—Shell ellipsoidal, with all three axes unequal or
irregular, sometimes becoming spiral. (Families 24-32.)[87]
{78}[Illustration: FIG. 24.—_Xiphacantha_ (Acantharia). From the surface.
The skeleton only, × 100, (From Wyville Thomson.)]
B. ACANTHARIA.
Order vii. ACTINELIDA.—Radial spines numerous, more than 20, usually
grouped irregularly. (Families 33-35.) _Xiphacantha_ Haeck.
Order viii. ACANTHONIDA.—Radial spines equal. (Families 36-38.)
Order ix. SPHAEROPHRACTA.—Radial spines 20, with a latticed spherical
shell, independent of, or formed from the reticulations of the spines.
(Families 39-41.) _Dorataspis_ Haeck. (Fig. 25, A).
Order x. PRUNOPHRACTA.—Radial spines 20, unequal; latticed shell,
ellipsoidal, lenticular, or doubly conical. (Families 42-44.)
C. NASSELLARIA.
Order xi. NASSOIDEA.—Skeleton absent. (Family 45.)
Order xii. PLECTOIDEA.—Skeleton of a single branching spicule, the
branches sometimes reticulate, but never forming a latticed shell or a
sagittal ring. (Families 46-47.)
Order xiii. STEPHOIDEA.—Skeleton with a sagittal ring continuous with
the branched spicule, and sometimes other rings or branches. (Families
48-51.) _Lithocercus_ Théel (Fig. 26, A).
Order xiv. SPYROIDEA.—Skeleton with a latticed shell developed around
the sagittal ring (cephalis), and constricted in the sagittal plane,
with a lower chamber (thorax) sometimes added. (Families 52-55.)
{79}Order xv. BOTRYOIDEA.—As in Spyroidea, but with the cephalis 3-4
lobed; lower chambers, one or several successively formed. (Families
56-58.)
Order xvi. CYRTOIDEA.—Shell as in the preceding orders, but without
lobing or constrictions. (Families 59-70.) _Theoconus_ Haeck. (Fig.
25, B).
D. PHAEODARIA.
Order xvii. PHAEOCYSTINA.—Skeleton 0 or of distinct spicules; capsule
centric. (Families 71-73.) _Aulactinium_ Haeck. (Fig. 26, B).
Order xviii. PHAEOSPHAERIA.—Skeleton a simple or latticed sphere, with
no oral opening (pylome); capsule central. (Families 74-77.)
Order xix. PHAEOGROMIA.—Skeleton a simple latticed shell with a pylome
at one end of the principal axis; capsule excentric, sub-apical.
(Families 78-82.) _Pharyngella_ Haeck.; _Tuscarora_ Murr.;
_Haeckeliana_ Murr. (Fig. 28).
Order xx. PHAEOCONCHIA.—Shell of two valves, opening in the plane
("frontal") of the three openings of the capsule. (Families 83-85.)
We exclude Haeckel's Dictyochida, with a skeleton recalling that of the
Stephoidea, but of the impure hollow substance of the Phaeodaria (p. 84).
They rank now as Silicoflagellates (p. 114).
The Radiolarian is distinguished from all other Protozoa by the chitinous
central capsule, so that its cytoplasm is separated into an outer layer,
the _extracapsular_ protoplasm (ectoplasm), and a central mass, the
_intracapsular_, containing the nucleus.[88]
The _extracapsular_ layer forms in its substance a gelatinous mass, of
variable reaction, through which the plasma itself ramifies as a network of
threads ("sarcodictyum"), uniting at the surface to constitute the
foundation for the pseudopodia. This gelatinous matter constitutes the
"calymma." It is largely vacuolated, the vacuoles ("alveoli"), of
exceptional size, lying in the nodes of the plasmic network, and containing
a liquid probably of lower specific gravity than seawater; and they are
especially abundant towards the surface, where they touch and become
polygonal. On mechanical irritation they disappear, to be formed anew after
an interval, a fact that may explain the sinking from the surface in
disturbed water. This layer may contain minute pigment granules, but the
droplets of oil and of albuminous matter frequent in the central layer are
rare here. {80}The "yellow cells" of a symbiotic Flagellate or Alga,
_Zooxanthella_, are embedded in the jelly of all except Phaeodaria, and the
whole ectosarc has the average consistency of a firm jelly.
The _pseudopodia_ are long and radiating, with a granular external layer,
whose streaming movements are continuous with those of the inner network.
In the Acantharia they contain a firm axial filament, like that of the
Heliozoa, which is traceable to the central capsule; and occasionally a
bundle of pseudopodia may coalesce to form a stout process like a flagellum
("sarcoflagellum"). Here, too, each spine, at its exit from the jelly, is
surrounded by a little cone of contractile filaments, the _myophrisks_,
whose action seems to be to pull up the jelly and increase the volume of
the spherical body so as to diminish its density.
[Illustration: FIG. 25.—Skeletons of _Radiolaria_. A, _Dorataspis_; B,
_Theoconus_. (After Haeckel.)]
The _intracapsular protoplasm_ is free from _Zooxanthella_ except in the
Acantharia. It is less abundantly vacuolated, and is finely granular. In
the Porulosa it shows a radial arrangement, with pyramidal stretches of
hyaline plasma separated by intervals rich in granules. Besides the alveoli
with watery contents, others are present with albuminoid matter in
solution. Oil-drops, often brilliantly coloured, occur either in the plasma
or floating in either kind of vacuole; and they are often luminous at
night. Added to these, the intracapsular plasm contains pigment-granules,
most frequently red or orange, {81}passing into yellow or brown, though
violet, blue, and green also occur. The "phaeodium,"[89] however, that
gives its name to the Phaeodaria, is an aggregate of dark grey, green, or
brown granules which are probably formed in the endoplasm, but accumulate
in the extracapsular plasm of the oral side of the central capsule.
Inorganic concretions and crystals are also found in the contents of the
central capsule, as well as aggregates of unknown composition, resembling
starch-grains in structure.
In the Monopylaea, or Nassellaria (Figs. 25, B, 26, A), the endoplasm is
differentiated above the perforated area of the central capsule into a cone
of radiating filaments termed the "porocone," which may be channels for the
communication between the exoplasm and the endoplasm, or perhaps serve, as
Haeckel suggests, to raise, by their contraction, the perforated area: he
compares them to the myophane striae of Infusoria. In the Phaeodaria (Fig.
26, B), a radiating laminated cone is seen in the outermost layer of the
endoplasm above the principal opening ("astropyle"), and a fibrillar one
around the two accessory ones ("parapyles"); and in some cases, continuous
with these, the whole outer layer of the endoplasm shows a meridional
striation.
The _nucleus_ is contained in the endoplasm, and is always at first single,
though it may divide again and again. The nuclear wall is a firm membrane,
sometimes finely porous. If there are concentric shells it at first
occupies the innermost, which it may actually come to enclose, protruding
lobes which grow through the several perforations of the lattice-work,
finally coalescing outside completely, so as to show no signs of the joins.
In the Nassellaria a similar process usually results in the formation of a
lobed nucleus, contained in an equally lobed central capsule. The chromatin
of the nucleus may be concentrated into a central mass, or distributed into
several "nucleoli," or it may assume the form of a twisted, gut-like
filament, or, again, the nuclear plasm may be reticulated, with the
chromatin deposited at the nodes of the network.
{82}[Illustration: FIG. 26.—A, _Lithocercus annularis_, with sagittal ring
(from Parker and Haswell). B, _Aulactinium actinastrum_. _C_, calymma;
_cent.caps._, _km_, central capsule; _Ext.caps.pr._, Extracapsular, and
_Int.caps.pr._, intracapsular protoplasm; _n_, _nu_, nucleus; _op_,
operculum; _ph_, phaeodium; _psd_, pseudopodium; _Skel._, skeleton; _z_,
Zooxanthella. (From Lang's _Comparative Anatomy_, after Haeckel.)]
The skeleton of this group varies, as shown in our conspectus, in the
several divisions.[90] The Acantharia (Figs. 24, 25, A) have a skeleton of
radiating spines meeting in the centre of figure of the endoplasm, and
forcing the nucleus to one side. The spines are typically 20 in number, and
emerge from the surface of the regular spherical forms (from which the
others may be readily derived) radially, in five sets of four in the
regions corresponding to the equator and the tropics and polar circles of
our world. {83}The four rays of adjacent circles alternate, so that the
"polar" and "equatorial" rays are on one set of meridians 90° apart, and
the "tropical" spines are on the intermediate meridians, as shown in the
figures. By tangential branching, and the meeting or coalescence of the
branches, reticulate (Figs. 23, 24, 25) and latticed shells are formed in
some families, with circles of openings or pylomes round the bases of the
spines. In the Sphaerocapsidae the spines are absent, but their original
sites are inferred from the 20 circles of pylomes.
In the Spumellaria the simplest form of the (siliceous) skeleton is that of
detached spicules, simple or complex, or passing into a latticed shell,
often with one or more larger openings (pylomes). Radiating spines often
traverse the whole of the cavity, becoming continuous with its latticed
wall, and bind firmly the successive zones when present (Fig. 23).
_Calcaromma calcarea_ was described by Wyville Thomson as having a shell of
apposed calcareous discs, and _Myxobrachia_, by Haeckel, as having
collections of the calcareous Coccoliths and Coccospheres. In both cases we
have to do with a Radiolarian not possessing a skeleton, but retaining the
undigested shells of its food, in the former case (_Actissa_) in a
continuous layer, in the latter (_Thalassicolla_) in accumulations that, by
their weight, droop and pull out the lower hemisphere into distinct arms.
The (siliceous) skeleton of the Nassellaria is absent only in the
Nassoidea, and is never represented by distinct spicules. Its simplest form
is a "tripod" with the legs downward, and the central capsule resting on
its apex. The addition of a fourth limb converts the tripod into a
"calthrop," the central capsule in this case resting between the upturned
leg and two of the lower three regarded as the "anterolateral"; the odd
lower leg, like the upturned one, being "posterior." Again, the skeleton
may present a "sagittal ring," often branched and spiny (Fig. 26, A), or
combined with the tripod or calthrop, or complicated by the addition of one
or more horizontal rings. Another type is presented by the "latticed
chamber" surrounding the central capsule, with a wide mouth ("pylome")
below. This is termed the "cephalis"; it may be combined in various ways
with the sagittal ring and the tripod or calthrop; and, again, it may be
prolonged by the addition of one, two, or three chambers below, {84}the
last one opening by a pylome (Fig. 25, B). These are termed "thorax,"
"abdomen," and "post-abdomen" respectively.
In the Phaeodaria the skeleton may be absent, spicular (of loose or
connected spicules) or latticed, continuous or bivalve. It is composed of
silica combined with organic matter, so that it chars when heated, is more
readily dissolved, and is not preserved in fossilisation. The spicules or
lattice-work are hollow, often with a central filament running in the
centre of the gelatinous contents. The latticed structure of the shell of
the Challengeridae (Fig. 28) is so fine as to recall that of the
Diatomaceae. In the Phaeoconchida the shell is in two halves, parted along
the "frontal" plane of the three apertures of the capsule.
[Illustration: FIG. 27.—Scheme of various possible skeletal forms deposited
in the meshes of an alveolar system, most of which are realised in the
Radiolaria. (From Verworn, after Dreyer.)]
The central capsule (rarely inconspicuous and difficult, if not impossible
to demonstrate) is of a substance which resembles chitin, though its
chemical reactions have not been fully studied hitherto, and indeed vary
from species to species. It is composed of a single layer, except in
_Phaeodaria_, where it is double. The operculum in this group, _i.e._ the
area around the aperture, is composed of an outer layer, which is radially
thickened, and a thin inner layer; the former is produced into the
projecting tube ("proboscis").
REPRODUCTION in the Radiolaria may be simple fission due to the binary
fission of the nucleus, the capsule, and the ectoplasm in succession. If
this last feature is omitted we have a colonial organism, composed of the
common ectoplasm containing numerous central capsules; and the genera in
which this occurs, all belonging to the Peripylaea, were formerly separated
(as Polycyttaria) from {85}the remaining Radiolaria (Monocyttaria). They
may either lack a skeleton (Collozoidae, Fig. 22), or have a skeleton of
detached spicules (Sphaerozoidae), or possess latticed shells
(Collosphaeridae) one for each capsule, and would seem therefore to belong,
as only differentiated by their colonial habit, to the several groups
having these respective characters. Fission has been well studied in
_Aulacantha_ (a Phaeodarian) by Borgert.[91] He finds that in this case the
skeleton is divided between the daughter-cells, and the missing part is
regenerated. In cases where this is impossible one of the daughter-cells
retains the old skeleton, and the other escapes as a bud to form a new
skeleton.
[Illustration: FIG. 28.—Shells of Challengeridae: A, _Tuscarora_; B,
_Pharyngella_; C, _Haeckeliana_. (From Wyville Thomson.)]
Two modes of reproduction by flagellate zoospores have been described (Fig.
22). In the one mode all the zoospores are alike—isospores—and frequently
contain a crystal of proteid nature as well as oil-globules. In the
Polycyttaria alone has the second mode of spore-formation been seen, and
that in the same species in which the formation of isospores occurs. Here
"anisospores" are formed, namely, large "mega-," and small
"micro-zoospores." They probably conjugate as male and female respectively;
but neither has the process been observed, nor has any product of such
conjugation (zygote) been recognised. In every case the formation of the
zoospores only involves the {86}endoplasm: the nucleus first undergoes
brood division, and the plasma within the capsule becomes concentrated
about its offspring, and segregates into the spores; the extracapsular
plasm disintegrates.[92]
The YELLOW CELLS (_Zooxanthella_), so frequently found in the Radiolaria
were long thought to be constituents of their body. Cienkowsky found that
when the host died from being kept in unchanged water, the yellow cells
survived and multiplied freely, often escaping from the gelatinised
cell-wall as biflagellate zoospores. The cell-wall is of cellulose. The
cell contains two chloroplastids, or plates coloured with the vegetal
pigment "diatomin." Besides ordinary transverse fission in the ordinary
encysted state in the ectoplasm of the host, when free they may pass into
what is known as a "_Palmella_-state," the cell-walls gelatinising; in this
condition they multiply freely, and constitute a jelly in which the
individual cells are seen as rounded bodies. They contain starch in two
forms—large hollow granules, not doubly refractive, and small solid
granules which polarise light. We may regard them as Chrysomonadaceae (p.
113). Similar organisms occur in many Anthozoa (see pp. 261, 339, 373 f.,
396). Diatomaceae (yellow Algae with silicified cell-walls) sometimes live
in the jelly of certain _Collosphaera_. Both these forms live in the state
known as "symbiosis" with their host; _i.e._ they are in mutually helpful
association, the Radiolarian absorbing salts from the water for the
nutrition of both, and the Alga or Flagellate taking up the CO_{2} due to
the respiration of the host, and building up organic material, the surplus
of which is doubtless utilised, at least in part, for the nutrition of the
host. A similar union between a Fungus and a coloured vegetal
("holophytic") organism is known as a Lichen.
The Suctorian Infusorian _Amoebophrya_ is parasitic in the ectoplasm of
certain Acantharia, and in the peculiar genus _Sticholonche_ which appears
to be intermediate between this group and Heliozoa.
The Silicoflagellate family Dictyochidae are found temporarily {87}embedded
in the ectoplasm of some of the Phaeocystina, and have a skeleton of
similar nature. Their true nature was shown by Borgert.
The Amphipod crustacean _Hyperia_[93] may enter the jelly of the colonial
forms, and feed there at will on the host.[94]
Haeckel, in his Monograph of the Radiolaria of the _Challenger_ enumerated
739 genera, comprising 4318 species; and Dreyer has added 6 new genera,
comprising 39 species, besides 7 belonging to known genera. Possibly, as we
shall see, many of the species may be mere states of growth, for it is
impossible to study the life-histories of this group; on the other hand, it
is pretty certain that new forms are likely to be discovered and described.
The Radiolaria are found living at all depths in the sea, by the
superficial or deep tow-net; and some appear to live near the bottom, where
the durable forms of the whole range also settle and accumulate. They thus
form what is known as Radiolarian ooze, which is distinguished from other
shallower deposits chiefly through the disappearance by solution of all
calcareous skeletons, as they slowly fell through the waters whereon they
originally floated at the same time with the siliceous remains of the
Radiolaria. The greatest wealth of forms is found in tropical seas, though
in some places in cold regions large numbers of individuals of a limited
range of species have been found.
Radiolaria of the groups with a pure siliceous skeleton can alone be
fossilised, even the impure siliceous skeleton of the Phaeodaria readily
dissolving in the depths at which they live: they have been generally
described by Ehrenberg's name _Polycystineae_. Tripolis (_Kieselguhr_) of
Tertiary ages have been found in many parts of the globe, consisting
largely or mainly of Radiolaria, and representing a Radiolarian ooze. That
of the Miocene of Barbados contains at least 400 species; that of Gruppe at
least 130. In Secondary and Palaeozoic rocks such oozes pass into
Radiolarian quartzites (some as recent as the Jurassic). They occur also in
fossilised excrement (coprolites), and in flint or chert concretions, as
far down as the lowest fossiliferous rocks, {88}the Cambrian. The older
forms are simple Sphaerellaria and Nassellaria. From a synopsis of the
history of the order in Haeckel's _Monograph_ (pp. clxxxvi.-clxxxviii.) we
learn that while a large number of skeletal forms had been described by
Ehrenberg, Huxley in 1851 published the first account of the living animal.
Since then our knowledge has been extended by the labours of Haeckel,
Cienkowsky, R. Hertwig, Karl Brandt, and A. Borgert.
5. PROTEOMYXA
_Sarcodina without a clear ectoplasm, whose active forms are amoeboid or
flagellate, or pass from the latter form to the former; multiplying
chiefly, if not exclusively, by brood-formation in a cyst. No complete
cell-pairing (syngamy) known, though the cytoplasms may unite into
plasmodia; pseudopodia of the amoeboid forms usually radiate or filose, but
without axial filaments. Saprophytic or parasitic in living animals or
plants._
This group is a sort of lumber-room for forms which it is hard to place
under Rhizopoda or Flagellata, and which produce simple cysts for
reproduction, not fructifications like the Mycetozoa. The cyst may be
formed for protection under drought ("hypnocyst"), or as a preliminary to
spore-formation ("sporocyst"). The latter may have a simple wall (simple
sporocyst), or else two or three formed in succession ("resting cyst"), so
as to enable it to resist prolonged desiccation, etc.: both differing from
the hypnocyst in that their contents undergo brood formation. On encystment
any indigestible food materials are extruded into the cyst, and in the
"resting cysts," which are usually of at least two layers, this faecal mass
lies in the space between them. The brood-cells escape, either as
flagellate-cells, resembling the simpler Protomastigina, called
"flagellulae," and which often become amoeboid (Fig. 29); or already
furnished with pseudopodia, and called "amoebulae," though they usually
recall _Actinophrys_ rather than _Amoeba_. In _Vampyrella_ and some others
the amoebulae fuse, and so attain a greater size, which is most probably
advantageous for feeding purposes. But usually it is as a uninucleate cell
that the being encysts. They may feed either by ingestion by the
pseudopodia, by the whole surface contained in a living host-cell, or by
passing a pseudopodium into a host-cell (Fig. 29 5). They may be divided as
follows:—
{89}A. MYXOIDEA.—Flagella 1-3; zoospores separating at once.
1. ZOOSPOREAE.—Brood-cells escaping as flagellulae, even if they become
amoeboid later. _Ciliophrys_ Cienk.; _Pseudospora_ Cienk. (Fig. 29).
2. AZOOSPOREAE.—Cells never flagellate. _Protomyxa_ Haeckel;
_Plasmodiophora_ Woronin; _Vampyrella_ Cienk.; _Serumsporidium_ L.
Pfeiffer.
B. CATALLACTA.—Brood-cells of cyst on liberation adhering at the centre
to form a spherical colony, multiflagellate; afterwards separating, and
becoming amoeboid. _Magosphaera_ Haeckel (marine).[95]
[Illustration: FIG. 29.—_Pseudospora lindstedtii._ 1, 2, Flagellate
zoospores; 3, young amoebula, with two contractile vacuoles, one being
reconstituted by three minute formative vacuoles; 4, 5, an amoebula
migrating to a fungus hypha through the wall of which it has sent a long
pseudopodium; 6, amoebula full-grown; 7, 8, mature cells rounded off,
protruding a flagellum, before encysting; 9, young sporocyst; 10, the
nucleus has divided into a brood of eight; 11-14, stages of formation of
zoospores. _cv_, Contractile vacuole; _e_, mass of faecal granules; _fl_,
flagellum; _n_, nucleus, × about 750/1.]
_Plasmodiophora_ infests the roots of Crucifers, causing the disease known
as "Hanburies," or "fingers and toes," in turnips, etc. _Serumsporidium_
dwells in the body cavity of small Crustacea. Many of this group were
described by Cienkowsky under the name of "Monadineae" (in _Arch. Mikr.
Anat._ i. 1865, p. 203). Zopf has added more than anyone else since then to
our knowledge. He monographed them under Cienkowsky's name, as a
subordinate group of the Myxomycetes, "_Pilzthiere oder Schleimpilze_," in
Schenk's _Handb. d. Bot._ vol. iii. pt. ii. (1887). To Lankester (_Encycl.
Brit._, reprint 1891) we owe the name here adopted. Zopf has successfully
pursued their study in recent {90}papers in his _Beitr. Nied. Org._ The
Chytridieae, usually ascribed to Fungi, are so closely allied to this group
that Zopf proposes to include at least the Synchytrieae herein.
This group is very closely allied to Sporozoa; for the absence of cytogamy,
and of sickle-germs,[96] and of the complex spores and cysts of the
Neosporidia, are the only absolute distinctions.
6. MYCETOZOA (MYXOMYCETES, MYXOGASTRES)
_Sarcodina moving and feeding by pseudopodia, with no skeleton, aggregating
more or less completely into complex "fructifications" before forming
1-nucleate resting spores; these may in the first instance liberate
flagellate zoospores, which afterwards become amoeboid, or may be amoeboid
from the first; zoospores capable of forming hypnocysts from which the
contents escape in the original form._
1. Aggregation taking place without plastogamy, zoospores amoeboid, with
a clear ectosarc
ACRASIEAE.
_Copromyxa_ Zopf; _Dictyostelium_ Brefeld.
2. Aggregation remaining lax, with merely thread-like connexions, except
when encystment is to take place; cytoplasm finely granular throughout;
complete fusion of the cytoplasm doubtful
FILOPLASMODIEAE.
_Labyrinthula_ Cienk.; _Chlamydomyxa_ Archer; _Leydenia_ (?) Schaud.
3. Plasmodium formation complete, eventuating in the formation of a
complex fructification often traversed by elastic, hygroscopic threads,
which by their contraction scatter the spores; zoospores usually
flagellate at first
MYXOMYCETES.
_Fuligo_ Hall.; _Chondrioderma_ Rostaf.; _Didymium_ Schrad. (Fig. 30).
I. The ACRASIEAE are a small group of saprophytes, often in the most
literal sense, though in some cases it has been proved that the actual food
is the bacteria of putrefaction. In them, since no cell-division takes
place in the fructification, it is certain that the multiplication of the
species must be due to the fissions of the amoeboid zoospores, which often
have the habit of _Amoeba limax_ (Fig. 1, p. 5).
II. FILOPLASMODIEAE.—_Chlamydomyxa_[97] is a not uncommon inhabitant of the
cells of bog-mosses and bog-pools, and its nutrition may be holophytic, as
it contains chromoplasts; but it {91}can also feed amoeba-fashion.
_Labyrinthula_ is marine, and in its fructification each of the component
cells forms four spores. _Leydenia_ has been found in the fluid of ascitic
dropsy, associated with malignant tumour.
III. MYXOMYCETES.—The fructification in this group is not formed by the
mere aggregation of the zoospores, but these fuse by their cytoplasm to
form a multinucleate body, the "plasmodium," which, after moving and
growing (with nuclear division) for some time like a great multinucleate
Reticularian, passes into rest, and develops a fructification by the
formation of a complex outer wall; within this the contents, after
multiplication of the nuclei, resolve themselves into uninucleate spores,
each with its own cyst-wall. The fructifications of this group are often
conspicuous, and resemble those of the Gasteromycetous fungi (_e.g._, the
Puffballs), whence they were at first called _Myxogastres_. De Bary first
discovered their true nature in 1859, and ever since they have been claimed
by botanist and zoologist alike.
The spore on germination liberates its contents as a minute flagellate,
with a single anterior lash and a contractile vacuole (Fig. 30, C). It soon
loses the lash, becomes amoeboid, and feeds on bacteria, etc. (Fig. 30, D,
E). In this state it can pass into hypnocysts, from which, as from the
spores, it emerges as a flagellula. After a time the amoeboids, which may
multiply by fission, fuse on meeting, so as to form the plasmodium (Fig.
30, F). This contains numerous nuclei, which multiply as it grows, and
numerous contractile vacuoles. When it attains full size it becomes
negatively hydrotactic, crawls to a dry place, and resolves itself into the
fructification. The external wall, and sometimes a basal support to the
fruit, are differentiated from the outer layer of protoplasm; while the
nuclei within, after undergoing a final bipartition, concentrate each
around an independent portion of plasma, which again is surrounded as a
spore by a cyst-wall. Often the maturing plasmodium within the wall of the
fruit is traversed by a network of anastomosing tubes filled with liquid,
the walls of which become differentiated into membrane like the fruit-wall,
and are continuous therewith. As the fruit ripens the liquid dries, and the
tubes now form a network of hollow threads, the "capillitium," often with
external spiral ridges (Fig. 30, A, B). These are very hygroscopic, and by
their expansion and contraction {92}determine the rupture of the fruit-wall
and the scattering of the spores.
[Illustration: FIG. 30.—_Didymium difforme._ A, two sporangia (_spg_ 1 and
2) on a fragment of leaf (_l_); B, section of sporangium, with ruptured
outer layer (_a_), and threads of capillitium (_cp_); C, a flagellula with
contractile vacuole (_c.vac_) and nucleus (_nu_); D, the same after loss of
flagellum; _b_, an ingested bacillus; E, an amoebula; F, conjugation of
amoebulae to form a small plasmodium; G, a larger plasmodium accompanied by
numerous amoebulae; _sp_, ingested spores. (After Lister.)]
Again, in some cases the plasmodia themselves aggregate in the same way as
the amoeboids do in the _Acrasieae_, and combine to form a compound fruit
termed an "aethalium,"[98] with the regions of the separate plasmodia more
or less clearly marked off. The species formerly termed _Aethalium
septicum_ is now known as _Fuligo varians_. It is a large and conspicuous
species, common on tan, and is a pest in the tanpits. Its aethalia may
reach a {93}diameter of a foot and more, and a thickness of two inches.
_Chondrioderma diffusum_, often utilised as a convenient "laboratory type,"
is common on the decaying haulms of beans in the late autumn. The interest
of this group is entirely biological, save for the "flowers of tan."[99]
{94}CHAPTER IV
PROTOZOA (_CONTINUED_): SPOROZOA[100]
II. Sporozoa.
_Protozoa parasitic in Metazoa, usually intracellular for at least part
of their cycle, rarely possessing pseudopodia, or flagella (save in the
sperms), never cilia; reproduction by brood-formation, often of
alternating types; syngamy leading up to resting spores in which minute
sickle-germs are formed, or unknown (Myxosporidiaceae)._
This group, of which seven years ago no single species was known in its
complete cycle, has recently become the subject of concentrated and
successful study, owing to the fact that it has been recognised to contain
the organisms which induce such scourges to animals as malarial fevers, and
various destructive murrains. Our earliest accurate, if partial knowledge,
was due to von Siebold, Kölliker, and van Beneden. Thirty years ago Ray
Lankester in England commenced the study of species that dwell in the
blood, destined to be of such moment for the well-being of man and the
animals in his service; and since then our knowledge has increased by the
labours of Manson, Ross and Minchin at home, Laveran, Blanchard, Thélohan,
Léger, Cuénot, Mesnil, Aimé Schneider in France, Grassi in Italy,
Schaudinn, Siedlecki, L. and R. Pfeiffer, Doflein in Central Europe, and
many others.
{95}[Illustration: FIG. 31.—_Lankesteria ascidiae_, showing life-cycle.
_a_, _b_, _c_, Sporozoites in digestive epithelium cells of host; _d_, _e_,
growth stages; _f_, free gregarine; _g_, association; _h_, encystment; _i_,
_j_, brood-divisions in associated mates; _k_, pairing-cells; _l_, syngamy;
_m_, zygote; _n_, _o_, _p_, nuclear divisions in spores; _q_, cyst with
adult spores, each containing 8 sickle-germs. (After Luhe, modified from
Siedlecki.)]
As a type we will take a simple form of the highest group, the
Gregarinidaceae, _Monocystis_, which inhabits the seminal vesicles of the
earthworm. In its youngest state, the "sporozoite," it is a naked,
sickle-shaped cell, which probably makes its way from the gut into one of
the large radial cells of the seminal funnel, where it attains its full
size, and then passes out into the vesicles or reservoirs of the semen, to
lie among the sperm morulae and young spermatozoa. The whole interior is
formed of the opaque endosarc, which contains a large central nucleus, and
is full of refractive granules of paramylum or paraglycogen,[101] a
carbohydrate allied to glycogen or animal starch, so common in the liver
and {96}muscles of Metazoa; besides these it contains proteid granules
which stain with carmine, and oil-drops. The ectosarc is formed of three
layers: (1) the outer layer or "cuticle"[102] is, in many cases if not
here, ribbed, with minute pores in the furrows, and is always porous enough
to allow the diffusion of dissolved nutriment; (2) a clear plasmatic layer,
the "sarcocyte"; (3) the "myocyte," formed of "myonemes," muscular fibrils
disposed in a network with transverse meshes, which effect the wriggling
movements of the cell. The endosarc contains the granules and the large
central nucleus. The adult becomes free in the seminal vesicles; here two
approximate, and surround themselves with a common cyst: a process which
has received the name of "association" (Fig. 31, _g-i_). Within this,
however, the protoplasms remain absolutely distinct. The nucleus undergoes
peculiar changes by which its volume is considerably reduced. When this
process of "nuclear reduction" is completed, each of the mates undergoes
brood-divisions (_j_), so as to give rise to a large number of rounded
naked 1-nucleate cells—the true pairing-cells. These unite two and two, and
so form the 1-nucleate spores (_k-m_), which become oat-shaped, form a
dense cyst-wall, and have been termed "pseudonavicellae" from their
likeness to the Diatomaceous genus _Navicella_. Some of the cytoplasm of
the original cells remains over unused, as "epiplasm," and ultimately
degenerates, as do a certain number of the brood-cells which presumably
have failed to pair. It is believed that the brood-cells from the same
parent will not unite together. The contents of each spore have again
undergone brood-division to form eight sickle-shaped zoospores, or
"sporozoites" (_n-q_), and thus the developmental cycle is completed.
Probably the spores, swallowed by birds, pass out in their excrement, and
when eaten by an earthworm open in its gut; the freed sickle-germs can now
migrate through the tissues to the seminal funnels, in the cells of which
they grow, ultimately becoming free in the seminal vesicles.[103]
{97}We may now pass to the classification of the group.
A. TELOSPORIDIA.—Cells 1-nucleate until the onset of brood-formation,
which is simultaneous.
1. GREGARINIDACEAE.—Cells early provided with a firm pellicle and
possessing a complex ectosarc; at first intracellular, soon becoming
free in the gut or coelom of Invertebrates. Pairing between adults,
which simultaneously produce each its brood of gametes, isogamous or
bisexual, which pair within the common cyst; zygotospores surrounded by
a firm cyst, and producing within a brood of sickle-shaped zoospores.
(i.) SCHIZOGREGARINIDAE.—Multiplying by simple fission in the free
state as well as by brood-formation; the brood-cells conjugating in a
common cyst, but producing only one pairing nucleus in each mate (the
rest aborting), and consequently only one spore.
_Ophryocystis_ A. Schn.
(ii.) ACEPHALINIDAE.—Cell one-chambered, usually without an epimerite
for attachment.
_Monocystis_ F. Stein; _Lankesteria_ Mingazzini.
(iii.) DICYSTIDAE.—Cell divided by a plasmic partition; epimerite
usually present.
_Gregarina_ Dufour; _Stylorhynchus_ A. Schn.; _Pterocephalus_ A.
Schn.
2. COCCIDIACEAE.—Cells of simple structure, intracellular in Metazoa.
Pairing between isolated cells usually sexually differentiated as
oosphere and sperm, the latter often flagellate. Brood-formation of the
adult cell giving rise to sickle-shaped zoospores (merozoites), or
progamic and producing the gametes. Oosperm motile or motionless,
finally producing a brood of spores, which again give rise to a brood
of sickle-spores.
(i.) COCCIDIIDAE.—Cell permanently intracellular, or very rarely
coelomic, encysting or not before division; zoospores always
sickle-shaped; oosperm encysting at once, producing spores with a
dense cell-wall producing sickle-germs.
(ii.) HAEMOSPORIDAE.—Cells parasitic in the blood corpuscles or free
in the blood of cold-blooded animals, encysting before
brood-formation; zoospores sickle-shaped; oosperm at first motile.
_Lankeresterella_ Labbé; (_Drepanidium_ Lank.;) _Karyolysus_ Labbé;
_Haemogregarina_ Danilewski.
(iii.) ACYSTOSPORIDAE.—Cells parasitic in the blood and haematocytes
of warm-blooded Vertebrates; never forming a cyst-wall before
dividing; zoospores formed in the corpuscles, amoeboid. Gametocytes
only forming gametes when taken into the stomach of insects. Oosperm
at first active, passing into the coelom, producing naked spores
which again produce a large brood of sickle zoospores, which migrate
to the salivary gland, and are injected with the saliva into the
warm-blooded host.
_Haemamoeba_ Grassi and Feletti; _Laverania_ Grassi and Feletti;
_Haemoproteus_ Kruse; _Halteridium_ Labbé.[104]
B. NEOSPORIDIA.—Cells becoming multinucleate apocytes before any
brood-formation occurs. Brood-formation progressive through the apocyte,
not simultaneous.
{98}1. MYXOSPORIDIACEAE.—Naked parasites in cold-blooded animals.
Spore-formation due to an aggregation of cytoplasm around a single
nucleus to form an archespore, which then produces a complex of cells
within which two daughter-cells form the spores and accessory
nematocysts.
_Myxidium_ Bütsch.; _Myxobolus_ Bütsch.; _Henneguya_ Thélohan;
_Nosema_ Nageli (= _Glugea_ Th.).
2. ACTINOMYXIDIACEAE.[105]—Apocyte resolved into a sporange, containing
eight secondary sporanges (so-called spores), of ternary symmetry and
provided with three polar nematocysts.
3. SARCOSPORIDIACEAE.—Encysted parasites in the muscles of Vertebrates,
with a double membrane; spores simple.
_Sarcocystis_ Lankester.
[Illustration: FIG. 32.—_Gregarina blattarum_ Sieb. A, two cephalonts,
embedded by their epimerite (_ep_), in cells of the gut-epithelium; _deu_,
deutomerite; nu, nucleus; _pr_, protomerite; B^1, B^2, two free specimens
of an allied genus; the epimerite is falling off in B^2, which is on its
way to become a sporont; C, cyst (_cy_) of A, with sporoducts (_spd_)
discharging the spores (_sp_), surrounded by an external gelatinous
investment (_g_). (From Parker and Haswell.)]
_Monocystis_ offers us the simplest type of GREGARINIDACEAE. In most
Gregarines (Figs. 31, 32) the sporozoite enters the epithelium-cell of the
gut of an Arthropod, Worm or Mollusc, and as it enlarges protrudes the
greater part of its bulk into the lumen, and may become free therein, or
pass into the coelom. The attached part is often enlarged into a sort of
grapple armed with spines, the "epimerite"; this contains only sarcocyte,
the other layers being absent. The freely projecting body is usually
divided by an ingrowth of the myocyte into a front segment ("protomerite"),
and a rear one ("deutomerite"), with the nucleus usually in the latter. In
this state the cell is termed a "cephalont." Conjugation is frequent, but
apparently is not always connected with {99}syngamy or spore-formation;
sometimes from two to five may be aggregated into a chain or "syzygy." The
number of cases in which a syngamic process between two cells has been
observed is constantly being increased. In _Stylorhynchus_ (Fig. 33) the
conjugation at first resembles that of _Monocystis_, but the actual
pairing-cells are bisexually differentiated into sperms in the one parent,
and oospheres in the other; it is remarkable that here the pear-shaped
sperms are apparently larger than the oospheres. In _Pterocephalus_ the
chief difference is that the sperms are minute.[106] In all cases of
spore-formation the epimerite is lost and the septum disappears; in this
state the cell is termed a sporont. Sometimes the epiplasm of the sporont
forms tubes ("sporoducts"), which project through the cyst-wall and give
exit to the spores, as in _Gregarina_ (Fig. 32, C), a parasite in the
beetle _Blaps_.
Gregarines infest most groups of Invertebrates except Sponges and perhaps
Coelenterates, the only exception cited being that of _Epizoanthus
glacialis_, a Zoantharian (p. 406). They appear to be relatively harmless
and are not known to induce epidemics.
The COCCIDIACEAE never attain so high a degree of cellular differentiation
as the Gregarines, which may be due to their habitat; for in the growing
state they are intracellular parasites. Their life-history shows a double
cycle, which has been most thoroughly worked out in COCCIDIIDAE by
Schaudinn and Siedlecki in parasites of our common Centipedes. We take that
of _Coccidium schubergi_ (in _Lithobius forficatus_[107]), beginning with
the sporozoite, which is liberated from the spores taken in with the food,
in the gut of the Centipede. This active sickle-shaped cell (Fig. 34, _l_)
enters an epithelial cell of the mid-gut, and grows therein till it attains
its full size (_a_), when it is termed a "schizont"; for it segments (Gk.
σχίζω, "I split") superficially into a large number of sickle-shaped
zoospores, the "merozoites" (_c_), resembling the sporozoites. The
segmentation is superficial, so that there may remain a large mass of
residual epiplasm. The merozoites are set free by the destruction of the
epithelium-cell in which they were formed, and which becomes disorganised,
like the residual epiplasm. Each merozoite may repeat the {100}behaviour of
the sporozoite, so that the disease spreads freely, and becomes acute after
several reinfections. After a time the adult parasites, instead of becoming
schizonts and simply forming merozoites by division, differentiate into
cells that undergo a binary sexual differentiation. Some cells, the
"oocytes" (_d_, _e_), escape into the gut, and the nucleus undergoes
changes by which some of its substance (or an abortive daughter-nucleus) is
expelled to the exterior (_f_), such a cell is now an "oogamete" or
oosphere. Others, again, are spermatogones (_h_): each when full grown on
escaping into the gut commences a division (_i_, _j_), like that of the
schizonts. The products of this division or segment-cells are the
flagellate sperms (_s_): they are more numerous and more minute than the
merozoites produced by the schizonts, and are attracted to the oosphere by
chemiotaxy (p. 23), and one enters it and fuses with it (_g_). The oosperm,
zygote or fertilised egg, thus formed invests itself with a dense
cyst-wall, as a "oospore" (_k_), its contents form one or more (2, 4, 8,
etc.) spores; and each spore forms again one, two, or four sickle-shaped
zoospores ("sporozoites"), destined to be liberated for a fresh cycle of
parasitic life when the spores are swallowed by another host.
[Illustration: FIG. 33.—Bisexual pairing of _Stylorhynchus_. _a_,
Spermatozoon; _b-e_, fusion of cytoplasm of spermatozoon and oosphere; _f_,
_g_, fusion of nuclei; _h-j_, development of wall to zygote; _k_, _l_,
formation of four sporoblasts; _l_, side view of spore; _m_, mature
sporozoites in spore. (After Léger.)]
{101}[Illustration: FIG. 34.—Life-history of _Coccidium schubergi_. _a_,
Penetration of epithelium-cell of host by sporozoite; _b-d_, stages of
multiple cell-formation in naked state (schizogony); _e_, _f_, formation of
oogamete; _g_, conjugation; _h-j_, formation of sperms (_s_); _k_,
development of zygote (fertilised ovum) to form four spores; _l_, formation
of two zoospores (or sickle germs) in each spore. (From Calkins's
_Protozoa_, after Schaudinn.)]
In some cases the oogametes are at first oblong, like ordinary merozoites,
and round off in the gut. The microgametocyte, or spermatogone, has the
same character, but is smaller; it applies itself like a cap to one pole of
the oogamete, which has rounded off; it then divides into four sperms,
whose cytoplasm is not sharply separated; one of these then separates from
the common mass, enters the oogamete, and so conjugation is effected, with
an oosperm as its result. This latter mode of conjugation is that of
_Adelea ovata_ and _Coccidium lacazei_: the former is probably the more
primitive and the commoner. The sperms {102}of Coccidiidae, when free,
usually possess two long flagella, either both anterior, or a very long one
in front and a short one behind, both turned backwards.
The genus _Coccidium_ affects many animals, and one species in particular,
_C. cuniculi_ Rivolta, attacks the liver of young rabbits,[108] giving rise
to the disease "coccidiosis." _Coccidium_ may also produce a sort of
dysentery in cattle on the Alpine pastures of Switzerland; and cases of
human coccidiosis are by no means unknown. _Coccidium_-like bodies have
been demonstrated in the human disease, "molluscum contagiosum," and the
"oriental sore" of Asia; similar bodies have also been recorded in smallpox
and vaccinia, malignant tumours and even syphilis, but their nature is not
certainly known; some of these are now referred to Flagellata (see p. 121).
Closely allied to the Coccidiidae are the HAEMOSPORIDAE, dwellers in the
blood of various cold-blooded Vertebrates,[109] and entering the corpuscles
as sporozoites or merozoites to attain the full size, when they divide by
schizogony; they are freed like those of the next family by the breaking up
of the corpuscle. The merozoites were described by Gaule (1879) as
"vermicles" ("Würmchen"), and regarded by him as peculiar
segregation-products of the blood; though Lankester had described the same
species in the Frog's blood as early as 1871, with a full recognition of
its true character. His name, _Drepanidium_, has had to give way, having
been appropriated to another animal, and has been aptly replaced by that of
_Lankesterella_. The sexual process of _Karyolysus_ has been found to take
place in a Tick, that of _Haemogregarina_ in a Leech, thus presenting a
close analogy to the next group, which only differs in its less definite
form in the active state, and in the lack of a cell-wall during
brood-formation.
Laveran was the first to describe a member of the {103}ACYSTOSPORIDAE, in
1880, as an organism always to be found in the blood of patients suffering
from malarial fever; this received the rather inappropriate name of
_Plasmodium_, which, by a pedantic adherence to the laws of priority, has
been used by systematists as a generic name. Golgi demonstrated the
coincidence of the stages of the intermittent fever with those of the
life-cycle of the parasite in the patient, the maturation of the schizont
and liberation of the sporozoites coinciding with the fits of fever.
Manson, who had already shown that the Nematodes of the blood that give
rise to Filarial haematuria (see Vol. II. p. 149) have an alternating life
in the gnats or mosquitos of the common genus _Culex_,[110] in 1896
suggested to Ronald Ross that the same might apply to this parasite, and
thus inspired a most successful work. The hypothesis had old prejudices in
its favour, for in many parts there was a current belief that sleeping
under mosquito-netting at least helped other precautions against malaria.
Ross found early in his investigations that _Culex_ was a good host for the
allied genus _Haemoproteus_ or _Proteosoma_, parasitic in birds, but could
neither inoculate man with fever nor be inoculated from man. He found,
however, that the malaria germs from man underwent further changes in the
stomach of a "dappled-wing mosquito," that is, as we have since learned, a
member of the genus _Anopheles_. Thenceforward the study advanced rapidly,
and a number of inquirers, including Grassi, Koch, MacCallum (who
discovered the true method of sexual union in _Halteridium_[111]), and Ross
himself, completed his discovery by supplying a complete picture of the
life-cycles of the malaria-germs. Unfortunately, there has been a most
unhappy rivalry as to the priority of the share in each fragment of the
discovery, whose history is summarised by Nuttall, we believe, with perfect
fairness.[112]
The merozoite is always amoeboid, and in this state enters the blood
corpuscle; herein it attains its full size, as a schizont, becoming filled
with granules of "melanin" or black pigment, probably a decomposition
product of the red colouring matter (haemoglobin).
{104}[Illustration: FIG. 35.—Life-history of Malarial Parasites. _A-G_,
Amoebula of quartan parasite to sporulation; _H_, its gametocyte; _I-M_,
amoebula of tertian parasite to sporulation; _N_, its gametocyte; _O_, _T_,
"crescents" or gametocytes of _Laverania_; _P-S_, sperm-formation; _U-W_,
maturation of oosphere; _X_, fertilisation; _Y_, zygote. _a_, Zygote
enlarging in gut of Mosquito; _b-e_, passing into the coelom; _f_, the
contents segmented into naked spores; _g_, the spores forming sickle-germs
or sporozoites; _h_, sporozoites passing into the salivary glands. (From
Calkins's _Protozoa_, after Ross and Fielding Ould.)]
The nucleus of the schizont now divides repeatedly, and then the schizont
segments into a flat brood of germs (merozoites), relatively few in the
parasite of quartan fever (_Haemamoeba malariae_, Fig. 35, E-G), many in
that of tertian (_H. vivax_, Fig. 35, M). These brood-cells escape and
behave for the most part as before. But after the disease has persisted for
some time we find that in the genus _Haemamoeba_, {105}which induces the
common malarial fevers of temperate regions, certain of the full-grown
germs, instead of behaving as schizonts, pass, as it were, to rest as round
cells; while in the allied genus _Laverania_, (_Haemomenas_, Ross) these
resting-cells are crescentic, with blunt horns, and are usually termed
half-moons (Fig. 35, O, T), characteristic of the bilious or pernicious
remittent fevers of the tropics and of the warmer temperate regions in
summer. These round or crescent-shaped cells are the gametocytes, which
only develop further in the drawn blood, whether under the microscope,
protected against evaporation, or in the stomach of the _Anopheles_: the
crescents become round, and then they, like the already round ones of
_Haemamoeba_, differentiate in exactly the same way as the corresponding
cells of _Coccidium schubergi_. The female cell only exhibits certain
changes in its nucleus to convert it into an oosphere: the male emits a
small number of sperms, long flagellum-like bodies, each with a nucleus;
and these, by their wriggling, detach themselves from the central core, no
longer nucleated. The male gametogonium with its protruded sperms was
termed the "_Polymitus_ form," and was by some regarded as a
degeneration-form, until MacCallum discovered that a "flagellum" regularly
undergoes sexual fusion with an oosphere in _Halteridium_, as has since
been found in the other genera. The oosperm (Y) so formed is at first
motile ("ookinete"), as it is in Haemosporidae, and passes into the
epithelium of the stomach of the gnat and then through the wall, acquiring
a cyst-wall and finally projecting into the coelom (_a-e_). Here it
segments into a number of spheres ("zygotomeres" of Ross) corresponding to
the Coccidian spores, but which never acquire a proper wall (_f_). These by
segmentation produce at their surface an immense quantity of elongated
sporozoites (the "zygotoblasts" or "blasts" of Ross, Fig. 35, _g_), these
are ultimately freed by the disappearance of the cyst-wall of the oosperm,
pass through the coelom into the salivary gland (_h_), and are discharged
with its secretion into the wound that the gnat inflicts in biting. In the
blood the blasts follow the ordinary development of merozoites in the blood
corpuscle, and the patient shows the corresponding signs of fever. This has
been completely proved by rearing the insect from the egg, feeding it on
the blood of a patient in whose blood there were ascertained to be the
germs of a definite species of {106}_Haemamoeba_, sending it to England,
where it was made to bite Dr. Manson's son, who had never had fever and
whose blood on repeated examination had proved free from any germs. In the
usual time he had a well-defined attack of the fever corresponding to that
germ, and his blood on examination revealed the _Haemamoeba_ of the proper
type. A few doses of quinine relieved him of the consequences of his mild
martyrdom to science. Experiments of similar character but of less rigorous
nature had been previously made in Italy with analogous results. Again, it
has been shown that by mere precautions against the bites of _Anopheles_,
and these only, all residents who adopted them during the malarious season
in the most unhealthy districts of Italy escaped fever during a whole
season; while those who did not adopt the precautions were badly
attacked.[113]
_Anopheles_ flourishes in shallow puddles, or small vessels such as tins,
etc., the pools left by dried-up brooks and torrents, as well as larger
masses of stagnant water, canals, and slow-flowing streams. Sticklebacks
and minnows feed freely on the larvae and keep down the numbers of the
species; where the fish are not found, the larvae may be destroyed by
pouring paraffin oil on the surface of the water and by drainage. A
combination of protective measures in Freetown (Sierra Leone) and other
ports on the west coast of Africa, Ismailia, and elsewhere, has met with
remarkable success during the short time for which it has been tried; and
it seems not improbable, that as the relatively benign intermittent fevers
have within the last century been banished from our own fen and marsh
districts, so the Guinea coast may within the next decade lose its sad
title of "The White Man's Grave."
So closely allied to this group in form, habit, and life-cycle are some
species of the Flagellate genus _Trypanosoma_, that in their less active
states they have been unhesitatingly placed here (see p. 119). Schaudinn
has seen Trypanosomic characters in the "blasts" of this group, which
apparently is the most primitive of the Sporozoa and a direct offshoot of
the Flagellates.
The MYXOSPORIDIACEAE (Fig. 36) are parasitic in various {107}cold-blooded
animals. They are at least binucleate in the youngest free state, and
become large and multinucleate apocytes, which may bud off outgrowths as
well as reproduce by spores. The spores of the apocyte are not produced by
simultaneous breaking up, but by successive differentiation. A single
nucleus aggregates around itself a limited portion of the cytoplasm, and
this again forms a membrane, becoming an archespore or a "pansporoblast,"
destined to produce two spores; within this, nuclear division takes place
so as to form about eight nuclei, two of which are extruded as abortive,
and of the other six, three are used up in the formation of each of the two
spores. Of these three nuclei in each spore, two form nematocysts, like
those of a Coelenterate (p. 246 f.), at the expense of the surrounding
plasm; while the third nucleus divides to form the two final nuclei of the
reproductive body. The whole aggregate of the reproductive body and the two
nematocysts is enveloped in a bivalve shell. In what we may call
germination, the nematocysts eject a thread that serves for attachment, the
valves of the shell open, and the binucleate mass crawls out and grows
afresh. _Nosema bombycis_ Nägeli (the spore of which has a single
nematocyst) is the organism of the "Pébrine" of the silkworm, which was
estimated to have caused a total loss in France of some £40,000,000 before
Pasteur investigated the malady and prescribed the effectual cure, or
rather precaution against its spread. This consisted in crushing each
mother in water after it had laid its eggs and seeking for pébrine germs.
If the mother proved to be infected, her eggs were destroyed, as the eggs
she had laid were certain to be also tainted. Balbiani completed the study
of the organism from a morphological standpoint. Some Myxosporidiaceae
produce destructive epidemics in fish.
[Illustration: FIG. 36.—A, _Myxidium lieberkühnii_, amoeboid phase; B,
_Myxobolus mülleri_, spore with discharged nematocysts (_ntc_); C, spores
(psorosperms) of a Myxosporidian. _ntc_, nematocysts. (From Parker and
Haswell.)]
{108}The DOLICHOSPORIDIA or SARCOSPORIDIACEAE are, in the adult state,
elongated sacs, often found in the substance of the voluntary muscles, and
known as "Rainey's" or "Miescher's Tubes"; they are at first uninucleate,
then multinucleate, and then break up successively into uninucleate cells,
the spores, in each of which, by division, are formed the sickle-shaped
zoospores.[114]
{109}CHAPTER V
PROTOZOA (_CONTINUED_): FLAGELLATA
III. Flagellata.
_Protozoa moving (and feeding in holozoic forms) by long flagella:
pseudopodia when developed usually transitory: nucleus single or if
multiple not biform: reproduction occurring in the active state and
usually by longitudinal fission, sometimes alternating with
brood-formation in the cyst or more rarely in the active state: form
usually definite: a firm pellicle or distinct cell-wall often present._
The Flagellates thus defined correspond to Bütschli's group of the
Mastigophora. The lowest and simplest forms, often loosely called "Monads,"
are only distinguishable from Sarcodina (especially Proteomyxa) and
Sporozoa by the above characters: their artificial nature is obvious when
we remember that many of the Sarcodina have a flagellate stage, and that
the sperms of bisexual Sporozoa are flagellate (as are indeed those of all
Metazoa except Nematodes and most Crustacea). Even as thus limited the
group is of enormous extent, and passes into the Chytridieae and
Phycomycetes Zoosporeae on the one hand, and by its holophytic colonial
members into the Algae, on the other.[115]
CLASSIFICATION.
A. Fission usually longitudinal (transverse only in a cyst), or if
multiple, radial and complete: pellicle absent, thin, or if armour-like,
with not more than two valves.
I. Food taken in at any part of the body by pseudopodia
1. PANTOSTOMATA
_Multicilia_ Cienk.; _Mastigamoeba_ F. E. Sch. (Fig. 37, 4).
{110}II. Food taken in at a definite point or points, or by absorption,
or nutrition holophytic.
1. No reticulate siliceous shell. Diameter under 500 µ (1/50").
* Contractile vacuole simple (one or more).
(α) Colourless: reserves usually fat: holozoic, saprophytic or
parasitic
2. PROTOMASTIGACEAE
(β) Plastids yellow or brown: reserves fat or proteid: nutrition
variable: body naked, often amoeboid in active state (_C. nudae_),
or with a test, sometimes containing calcareous discs
("coccoliths," "rhabdoliths") of peculiar form (_C. loricatae_)
3. CHRYSOMONADACEAE
_Chromulina_ Cienk.; _Chrysamoeba_ Klebs; _Hydrurus_ Ag.
_Dinobryon_ Ehrb. (Fig. 37, 11); _Syncrypta_ Ehrb. (Fig. 37, 12);
_Zooxanthella_ Brandt; _Pontosphaera_ Lohm.; _Coccolithophora_
Lohm.; _Rhabdosphaera_ Haeck.
(γ) Green, (more rarely yellow or brown) or colourless: reserves
starch: fission longitudinal
4. CRYPTOMONADACEAE
_Cryptomonas_ Ehrb. (Fig. 37, 9); _Paramoeba_ Greeff.
(δ) Green (rarely colourless): fission multiple, radial
5. VOLVOCACEAE
** System of contractile vacuoles complex, with accessory formative
vacuoles or reservoir, or both.
(ε) Pellicle delicate or absent: pseudopodia often emitted:
excretory pore distinct from flagellar pit: reserves fat
6. CHLOROMONADACEAE
_Chloramoeba_ Lagerheim; _Thaumatomastix_, Lauterborn.
(ζ) Pellicle dense, tough or hard, often wrinkled or striate:
contractile vacuole discharging by the flagellar pit. Nutrition
variable
7. EUGLENACEAE
_Euglena_ Ehrb.; _Astasia_ Duj. (Fig. 37, 3); _Anisonema_ Duj.;
_Eutreptia_ Perty (Fig. 42, p. 124); _Trachelomonas_ Ehrb. (Fig.
37, 1); _Cryptoglena_ Ehrb.
2. Skeleton an open network of hollow siliceous spicules. Plastids
yellow. Diameter under 500 µ.
8. SILICOFLAGELLATA
_Dictyocha_ Ehrb.
3. Diameter over 500 µ. Mouth opening into a large reticulate
endoplasm: flagella 1, or 2, very unequal.
9. CYSTOFLAGELLATA
_Noctiluca_ Suriray (Fig. 48); _Leptodiscus_ R. Hertw.
B. Fission oblique or transverse: flagella two, dissimilar, the one
coiled round the base of the other or in a traverse groove; pellicle
often dense, of numerous armour-like plates
10. DINOFLAGELLATA
_Ceratium_ Schrank; _Gymnodinium_ Stein; _Peridinium_ Ehrb. (Fig. 46);
_Pouchetia_ Schütt; _Pyrocystis_ Murray (Fig. 47); _Polykrikos_ Bütschli.
The Protomastigaceae and Volvocaceae are so extensive as to require further
subdivision.
PROTOMASTIGACEAE
I. Oral spots 2. Flagella distant in pairs. DISTOMATIDAE
II. Oral spot 1 or 0.
{111}A. Flagellum 1.
(_a_) No anterior process: often parasitic
OIKOMONADIDAE
_Oikomonas_ K. (Figs. 37, 2, 8); _Trypanosoma_ Gruby (Fig. 39, _a-f_);
_Treponema_ Vuill. (Fig. 39, _g-i_).
(_b_) Anterior process unilateral or proboscidiform: cell often thecate
BICOECIDAE
_Bicoeca_ Clark; _Poteriodendron_ St.
(_c_) Anterior process a funnel, surrounding the base of the flagellum:
cells often thecate.
(i.) Funnel free
CRASPEDOMONADIDAE
_Codosiga_ Clark; _Monosiga_ Cl.; _Polyoeca_ Kent; _Proterospongia_
Kent; _Salpingoeca_ Cl.
(ii.) Funnel not emerging from the general gelatinous investment
PHALANSTERIDAE
B. Flagella 2, unequal or dissimilar in function, the one sometimes short
and thick.
(_a_) Both flagella directed forwards
MONADIDAE
_Monas_ St.; _Anthophysa_ Bory (Fig. 37, 13).
(_b_) One flagellum, usually the longer, turned backwards
BODONIDAE
_Bodo_ St. (Fig. 38).
C. Flagella 2, equal and similar
AMPHIMONADIDAE
_Amphimonas_ Duj.; _Diplomita_ K. (Fig. 37, 10); _Rhipidodendron_ St.
(Fig. 37, 14).
D. Flagella 3
TRIMASTIGIDAE
_Dallingeria_ K. (Fig. 37, 6); _Costia_ Leclercq.
E. Flagella 4 or more: mostly parasitic in Metazoa
POLYMASTIGIDAE
_Trichomonas_ Donne; _Tetramitus_ Perty (Fig. 37, 7); _Hexamitus_ Duj.;
_Lamblia_ Blanchard.
F. Flagella numerous, sometimes constituting a complete ciliiform
investment, and occasionally accompanied by an undulating membrane:
parasitic in Metazoa.
(_a_) Flagella long: nucleus single: parasitic in insects
TRICHONYMPHIDAE
_Dinenympha_ Leidy; _Joenia_ Grassi; _Pyrsonympha_ Leidy;
_Trichonympha_ Leidy; _Lophomonas_ St.; _Maupasia_ Schew.
(_b_) Flagella short, ciliiform, uniformly distributed: nuclei very
numerous, all similar: parasitic in Amphibia
OPALINIDAE
_Opalina_ Purkinje and Valentin (Fig. 41).
VOLVOCACEAE
A. Cells usually isolated, separating after fission or brood-formation.
Usually green (sometimes red), more rarely colourless saprophytes
CHLAMYDOMONADIDAE
_Chlamydomonas_ Ehrb.; _Phacotus_ Perty; _Polytoma_ Ehrb.; _Sphaerella_
Sommerf. (Fig. 43); _Zoochlorella_.
B. Cells multiplying in the active state by radial divisions in the same
plane and usually incurving to form a spherical colony, united in a
gelatinous investment, sometimes traversed by plasmic threads
VOLVOCIDAE
_Gonium_ O.F.M.; _Eudorina_ Ehrb.; _Pandorina_ Bory (Fig. 45);
_Stephanosphaera_ Cohn; _Volvox_ L. (Fig. 44).
{112}[Illustration: FIG. 37.—Various forms of Flagellata. 2, 6-8, 10, 13,
14, Protomastigaceae; 11, 12, Chrysomonadaceae; 9, Cryptomonadaceae; 1, 3,
Euglenaceae; 4, Pantostomata: note branched stalk in 13; branched tubular
theca in 14; distinct thecae in 11; stalk and theca in 10. In 2, flagellate
(_a_) and amoeboid (_b_) phases are shown; in 5, flagellate (_a_) and
Heliozoan (_b_) phases[116]; in 8 are shown two stages in the ingestion of
a food particle (_f_); _chr_, plastoids; _c.vac_, contractile vacuole; _f_,
food particle; _g_, gullet; _l_, theca; _nu_, nucleus; _p_, protoplasm;
_per_, peristome; _v.i_, vacuole of ingestion. (From Parker and Haswell,
mostly from Bütschli's _Protozoa_.)]
{113}The modes of nutrition are threefold: the simplest forms live in
liquids containing decaying organic matter which they absorb through their
surface ("saprophytic"): others take in food either _Amoeba_ fashion, or
into a vacuole formed for the purpose, or into a definite mouth
("holozoic"): others again have coloured plastids, green or brown or yellow
("holophytic"), having the plant's faculty of manufacturing their own
food-supply. But we meet with species that show chromatophores at one time
and lack them at another; or, again, the same individual (_Euglena_) may
pass from holozoic life to saprophytic (_Paramoeba_, some Dinoflagellates)
as conditions alter.
Many secrete a stalk at the hinder end: by "continuous" formation of this,
without rupture at fission, a branching colony is formed (_Polyoeca_). This
stalk may have a varying consistency. In _Anthophysa_ (Fig. 37, 13) it
appears to be due to the welding of excrementitious particles voided at the
hinder end of the body with a gelatinous excretion; but the division of the
stalk is here occasional or intermittent, so that the cells are found in
tufts at the apex of the branches. A corresponding secretion, gelatinous or
chitinous, around the body of the cell forms a cup or "theca," within which
the cell lies quite free or sticking to it by its surface, or attached to
it by a rigid or contractile thread. The theca, again, may assume the form
of a mere gelatinous mass in which the cell-bodies may be completely
plunged, so that only the flagella protrude, as in Volvocidae,
_Proterospongia_ (Fig. 75, p. 182), and _Rhipidodendron_ (Fig. 37, 14).
Often this jelly assumes the form of a fan (_Phalansterium_), the branching
tubes of which it is composed lying for some way alongside, and ultimately
diverging. In _Hydrurus_, the branching jelly assumes the form of a
branching Confervoid.[117]
The cell-body may be bounded by an ill-defined plasmatic layer in
Chrysomonadaceae and some Protomastigaceae,[118] or it may form a plasmatic
membrane or "pellicle," sometimes very firm and tough, or striated as in
Euglenaceae, or it may have a separate "cuticle" (in the holophytic species
formed of cellulose), or even a bivalve or multivalve shell of distinct
plates, hinged or overlapping (_Cryptoglena_, _Phacotus_, Dinoflagellates).
The wall of the {114}Coccolithophoridae, a family of Chrysomonadaceae, is
strengthened by embedded calcareous spicules ("coccoliths," "cyatholiths,"
"rhabdoliths"), which in the most complex forms (cyatholiths) are like a
shirt-stud, traversed by a tube passing through the stem and opening at
both ends. These organisms[119] constitute a large proportion of the
plankton; the spicules isolated, or in their original state of aggregation
("coccospheres," "rhabdospheres"), enter largely into the composition of
deep-sea calcareous oozes. They occur fossil from Cambrian times (Potsdam
sandstone of Michigan and Canada), and are in some strata extremely
abundant, 800,000 occurring to the mm. cube in an Eocene marl.
The Silicoflagellates have siliceous skeletons resembling that of many
_Radiolaria_, to which they were referred until the living organism was
described (see pp. 79, 86 f.).
The flagellum has been shown by Fischer to have one of two forms: either it
is whip-like, the stick, alone visible in the fresh specimen, being seen
when stained to be continued into a long lash, hitherto invisible; or the
whole length is fringed with fine ciliiform lateral outgrowths. If single
it is almost always protruded as a tugging organ ("tractellum");[120] the
chief exceptions are the Craspedomonads, where it is posterior and acts as
a scull ("pulsellum"), and some Dinoflagellates, where it is reversible in
action or posterior. In addition to the anterior flagellum there may be one
or more posterior ones, which trail behind as sense organs, or may anchor
the cell by their tips. _Dallingeria_ has two of these, and _Bodo saltans_
a single anterior anchoring lash, by which they spring up and down against
the organic débris among which they live, and disintegrate it. The numerous
similar long flagella of the Trichonymphidae afford a transition in the
genus _Pyrsonympha_ to the short abundant cilia of _Opalina_, usually
referred to the Ciliate Infusoria.
{115}An undulating membrane occurs, sometimes passing into the flagellum in
certain genera, all parasitic, such as _Trypanosoma_ (incl.
_Herpetomonas_), _Trichomonas_, _Hexamitus_, and _Dinenympha_.
In some cases the flagellum (or flagella) is inserted into a definite pit,
which in allied forms is the mouth-opening. The contractile vacuole is
present in the fresh-water forms, but not in all the marine ones, nor in
the endoparasites. It may be single or surrounded by a ring of minute
"formative" vacuoles or discharge into a permanently visible "reservoir."
This again may discharge directly to the surface or through the pit or
canal in which the flagellum takes origin (_Euglena_).
The "chromatophore" may be a single or double plate, or multiple.[121] In
the peculiar form _Paramoeba_ the chromatophore may degenerate and be
reproduced anew. It often encloses rounded or polygonal granules of
uncoloured plasma, very refractive, known as "pyrenoids." These, like the
chromatophores, multiply by direct fission. The "reserves" may be (1)
fat-globules; (2) granules of a possibly proteid substance termed
"leucosin"; (3) a carbohydrate termed "paramylum," differing slightly from
starch (see p. 95); (4) true starch, which is usually deposited in minute
granules to form an investment for the pyrenoid when such is present.
A strongly staining granule is usually present in the plasma near the base
of the flagellum. This we may term a "blepharoplast" or a "centrosome" in
the wider sense.
FISSION is usually longitudinal in the active state; a few exceptions are
recorded. Encystment is not uncommon; and in the coloured forms the
cyst-wall is of cellulose. Division in the cyst is usually multiple;[122]
in the coloured forms, however, vegetative growth often alternates with
division, giving rise to plant-like bodies. _Polytoma_ and other
Chlamydomonadidae multiply by "brood-formation" in the active state; the
blepharoplast, as Dangeard suggests, persisting to continue the motion of
the flagella of the parent, while the rest of the plasm divides to form the
brood. CONJUGATION has been observed in many species. In some species of
_Chlamydomonas_ it takes place after one or both of the two {116}cells have
come to rest, but in most cases it occurs between active cells. We find
every transition between equal unions and differentiated sexual unions, as
we shall see in discussing the Volvocaceae.[123] The "coupled-cell" differs
in behaviour in the different groups, but almost always goes to rest and
encysts at once, whatever it may do afterwards.
The LIFE-HISTORY of many Flagellates has been successfully studied by
various observers, and has shed a flood of light on many of the processes
of living beings that were hitherto obscure. The first studies were carried
through by the patient labours of Drysdale and Dallinger. A delicate
mechanical stage enabled the observer to keep in the field of view a single
Flagellate, and, when it divided into two, to follow up one of the
products. A binocular eye-piece saved much fatigue, and enabled the
observers to exchange places without losing sight of the special Flagellate
under observation; for the one who came to relieve would put one eye to the
instrument and recognise the individual Flagellate under view as he passed
his hand round to the mechanism of the stage before the first watcher
finally relinquished his place at the end of the spell of work.
Spoon-feeding by Mrs. Dallinger enabled such shifts to be prolonged, the
longest being one of nine hours by Dr. Dallinger.
{117}[Illustration: FIG. 38.—_Bodo saltans._ A, the positions assumed in
the springing movements of the anchored form; B, longitudinal fission of
anchored forms; C, transverse fission of the same; D, fission of
free-swimming form; E^1-E^4, conjugation of free-swimming with anchored
form; E^5, zygote; E^6, emission of spores from zygote; F, growth of
spores: _c.vac_, contractile vacuole; _fl.1_, anterior; _fl.2_, ventral
flagellum; _nu_, nucleus. (From Parker's _Biology_, after Dallinger.)]
The life-cycles varied considerably in length. It was in every case found
that after a series of fissions the species ultimately underwent
conjugation (more or less unequal or bisexual in character);[124] the
zygote encysted; and within the cyst the protoplasmic body underwent
brood-formation, the outcome of which was a mass of {118}spores discharged
by the rupture of the cyst (Fig. 38). These spores grow from a size too
minute for resolution by our microscopes into the ordinary flagellate form.
They withstand the effects of drying, if this be effected immediately on
their escape from the ruptured cyst; so that it is probable that each spore
has itself a delicate cyst-wall and an aplanospore, from which a single
zoospore escapes. The complex cycle, of course, comprises the whole course
from spore-formation to spore-formation. Such complete and regular
"life-histories," each characteristic of the species, were the final
argument against those who held to the belief that spontaneous generation
of living beings took place in infusions of decomposing organic matter.
Previous to the work of these observers it had been almost universally
believed that the temperature of boiling water was adequate to kill all
living germs, and that any life that appeared in a closed vessel after
boiling must be due to spontaneous change in its contents. But they now
showed that, while none of the species studied resisted exposure _in the
active condition_ to a temperature of 138°-140° F., the spores only
succumbed, in liquid, to temperatures that might even reach 268° F., or
when dry, even 300° F. or more. Such facts explain the constant occurrence
of one or more such minute species in liquids putrefying under ordinary
conditions, the spores doubtless being present in the dust of the air. Very
often several species may co-exist in one infusion; but they separate
themselves into different zones, according to their respective need for
air, when a drop of the liquid is placed on the slide and covered for
examination. Dallinger[125] has made a series of experiments on the
resistance of these organisms in their successive cycles to a gradual rise
of temperature. Starting with a liquid containing three distinct species,
which grew and multiplied normally at 60° F., he placed it under conditions
in which he could slowly raise the temperature. While all the original
inmates would have perished at 142° F., he succeeded in finally producing
races that throve at 158° F., a scalding heat, when an accident put an end
to that series of experiments. In no instance was the temperature raised so
much as to kill off the beings, so that the increased tolerance of their
descendants was due not, as might have been anticipated, to selection of
those that best resisted, but to the inheritance of {119}an increased
toleration and resistance from one generation or cycle to another.
As we noted above (p. 40), the study of the Flagellates has been largely in
the hands of botanists. After the work of Bütschli in Bronn's
_Thier-Reich_, Klebs[126] took up their study; and the principal monographs
during the last decade have appeared in Engler and Prantl's
_Pflanzenfamilien_, where Senn[127] treats the Flagellates generally,
Wille[128] the Volvocaceae, and Schütt the "Peridiniales" or
Dinoflagellata;[129] while only the Cystoflagellata, with but two genera,
have been left to the undisputed sway of the zoologists.[130]
Among this group the majority are saprophytes, found in water containing
putrefying matter or bacteria. The forms so carefully studied by Dallinger
and Drysdale belong to the genera _Bodo_, _Cercomonas_, _Tetramitus_,
_Monas_, and _Dallingeria_. Many others are parasites in the blood or
internal cavities of higher animals, some apparently harmless, such as
_Trichomonas vaginalis_, parasitic in man, others of singular malignity.
_Costia necatrix_, infesting the epithelial scales of fresh-water fish,
often devastates hatcheries. The genus _Trypanosoma_, Gruby, contributes a
number of parasites, giving rise to deadly disease in man and beast.[131]
_T. lewisii_ is common in Rodents, but is relatively harmless. _T. evansii_
is the cause of the Surra disease of Ruminants in India, and is apparently
communicated by the bites of "large brown flies" (almost certainly Breeze
Flies or Tabanidae, Vol. VI. p. 481). _T. brucei_, transferred to cattle by
the Tsetse Fly, _Glossina morsitans_ (see Vol. VI. Fig. 244, p. 513) in
Equatorial Africa, is the cause of the deadly Nagana disease, which renders
whole tracts of country impassable to ox or horse. Other Trypanosomic
diseases of animals are, in Algeria and the Punjab, "dourine," infecting
horses and dogs; in South America, Mal de Caderas (falling-sickness), an
epidemic paralysis of cattle. During the printing of this book, much
additional knowledge has been gained on this genus and the diseases it
engenders. The Trypanosomic {120}fever recently recognised on the West
Coast has been found to be the early stage of the sleeping-sickness, that
well-known and most deadly epidemic of Tropical Africa. Through the
researches of Castellani, Nabarro, and especially Colonel and Mrs. Bruce,
we know now that the parasite _T. gambiense_ is transferred by an
intermediate host, a kind of Tsetse Fly (_Glossina palpalis_). Schaudinn's
full study of a parasite of the blood corpuscles of the Owl has shown that
while in its intracorpuscular state it resembles closely the malarial
parasites in behaviour, and in its schizogenic multiplication, so that it
was considered an Acystosporidian, under the name of _Halteridium_, it is
really a _Trypanosoma_;[132] for the accomplishment of successful sexual
reproduction it requires transference to the gut of a gnat (_Culex_). The
germs may infect the ovary, and give the offspring of the insect the innate
power of infecting Owls. Thus a new light is shed on the origin of the
Coccidiaceae, whose "blasts" in the insect host resemble _Trypanosoma_ in
their morphology.
[Illustration: FIG. 39.—Morphology of _Trypanosoma_. _a-f_, Stages in
development of _Trypanosoma noctuae_ from the active zygote ("ookinete");
_b_, first division of nucleus into larger (trophic) and smaller (kineto-)
nucleus; _c_, _d_, division of smaller nucleus and its transformations to
form "blepharoplast" and myonemes; _f_, adult _Trypanosoma_; _g_, _h_, _i_,
_Treponema zeemannii_ of Owl; _g_, Trypanosome form; _h_, _Spirochaeta_
form; _i_, rosette aggregate. (After Schaudinn.)]
The human Tick fever of the Western United States and the epizootic Texas
fever are known to be due to blood parasites of the genus _Piroplasma_
(_Babesia_), of which the free state is that of a Trypanosome. It appears
certain that Texas fever, though due to Tick bites, is not transferred
directly from one beast to another by the same Tick; but the offspring of a
female Tick that has sucked an infected ox contains Trypanosome germs, and
will by their bites infect other animals. {121}It would seem probable that
the virulence of the Persian Tick (_Argas persica_) is due to similar
causes. The Indian maladies known as "Kala Azar" and "Oriental Sore" are
characterised by blood parasites, at first called after their discoverer
the "Leishman bodies," which have proved to be the effects of a
_Piroplasma_.
_Trypanosoma_ is distinguished by the expansion of its flagellum into an
undulating membrane, that runs down the edge of the body, and may project
behind as a second lash. In this membrane run eight fine muscular
filaments, or myonemes, four on either surface, within the undulating
membrane; at their lower end they are all connected with a rounded body,
the "blepharoplast," which is here in its origin, as well as in its
behaviour in reproductive processes, a true modified nucleus, comparable in
some respects, as was first noted by Plimmer and Rose Bradford,[133] with
the micronucleus of the Infusoria. Part of the segmentation spindle
persists in the form of a filament uniting the blepharoplast with the large
true functional nucleus (Fig. 39, _a-f_).
The blood of patients suffering from relapsing fever contains a fine
wriggling parasite, which was described as a Schizomycete, allied to the
bacteria, and hitherto termed _Spirochaeta obermeieri_. Schaudinn has shown
that this and other similar blood parasites are closely allied to
_Trypanosoma_; and since the original genus was founded on organisms of
putrefaction which are undoubtedly Schizomycetes, Vuillemin has suggested
the name _Treponema_. _T. pallidum_ is found in syphilitic patients, and
appears to be responsible for their illness.[134]
The Craspedomonadidae (often called Choanoflagellates, Fig. 40) are a group
whose true nature was elucidated some forty years ago by the American
zoologist, H. James-Clark. They are attached either to a substratum, by a
stalk produced by the base of the cell, or to other members of the same
colony; they are distinguished by the protrusion of the cytoplasm around
the base of the single flagellum into a pellucid funnel,[135] in which the
plasma is in constant motion, though the funnel retains its shape and size,
except when, as sometimes happens, it is retracted.
{122}[Illustration: FIG. 40.—Various forms of Craspedomonadidae. 2, _a_,
Adult cell; 2, _b_, longitudinal fission; 2, _c_, the production of
flagellulae by brood-formation; _c_, collar; _c.vac_, contractile vacuole;
_fl_, flagellum; _l_, theca; _nu_, nucleus; _s_, stalk. (After Saville
Kent.)]
The agitation of the flagellum determines a stream of water upwards along
the outer walls of the funnel; and the food-particles brought along adhere
to the outside of the funnel, and are carried by its streaming movement to
the basal constriction, where they are swallowed by the plasma, which
appears to form a swallowing vacuole at that point. Longitudinal fission is
the ordinary mode of reproduction, extending up through the funnel. If the
two so formed continue to produce a stalk, the result is the formation of a
tree-like stem, whose twigs bear at the ends the funnelled cells, or
"collar-cells" as they are usually called. In _Salpingoeca_, as in so many
other Flagellates, each cell forms a cup or theca, often of most graceful
vase-like outline, the rim being elegantly turned back. _Proterospongia_
(Fig. 75, p. 182) secretes a gelatinous investment for the colony, which is
attached to solid bodies. In this species, according to Saville Kent, the
central members of the colony retract their collar, lose their flagellum,
become amoeboid, and finally undergo brood-formation to produce minute
zoospores. This is the form which by its differentiation recalls the
Sponges, and has been regarded as a {123}transition towards them; for the
flagellate, nutritive cells of the Sponges are provided with a collar,
which exists in no other group of Metazoa (see pp. 171, 181, and Fig. 70,
p. 176). The most recent monographer of the family is Raoul Francé, but
James-Clark and Saville Kent did the pioneering work.
[Illustration: FIG. 41.—_Opalina ranarum._ A, living specimen; B, stained
specimen showing nuclei; C, stages in nuclear division; D-F, stages in
fission; G, final product of fission; H, encysted form; I, young form
liberated from cyst; K, the same after multiplication of the nucleus has
begun. _nu_, Nucleus. (From Parker's _Biology_, after Saville Kent and
Zeller.)]
Of the life-history of the Trichonymphidae,[136] all of which are parasitic
in the alimentary canal of Insects, especially Termites or White Ants (Vol.
V. p. 356), nothing is known. Some of them have a complete investment of
motile flagella, like enormously long cilia, which in _Dinenympha_ appear
to coalesce into four longitudinal undulating membranes. _Lophomonas_
inhabits the gut of the Cockroach and Mole-cricket. The Opalinidae have
also a complete investment of cilia, which are short, and give the aspect
of a Ciliate to the animal, which is common in the rectum of Amphibia, and
dies when transferred to water. But despite the outward resemblance, the
nuclei, of which there may be as many as 200, are all similar, and
consequently this group cannot be placed among the Infusoria at all.
_Opalina_ has no mouth nor contractile vacuole. It multiplies by dividing
{124}irregularly and at intervals, resolving finally into 1-nucleate
fragments, which encyst and pass into the water. When swallowed the cyst
dissolves, its contents enlarge, and ultimately assume the adult form.[137]
_Maupasia_ has a partial investment of cilia, a single long flagellum and
mouth, a contractile vesicle, and a single simple nucleus. It seems to find
an appropriate place near the two above groups, though it is free, and
possesses a mouth.
[Illustration: FIG. 42.—Longitudinal Fission of _Eutreptia viridis_
(Euglenaceae), showing chloroplasts, nucleus, and flagella arising from
pharynx-tube. (After Steuer.)]
Among the Euglenaceae, _Euglena viridis_ is a very common form, giving the
green colour to stagnant or slow-flowing ditches and puddles in light
places, especially when contaminated by a fair amount of dung, as by the
overflow of a pig-sty, in company with a few hardy Rotifers, such as
_Hydatina senta_ (Vol. II. Fig. 106, p. 199) and _Brachionus_. _Euglena_ is
about 0.1 mm. in length when fully extended, oval, pointed behind,
obliquely truncate in front, with a flagellum arising from the pharyngeal
pit. It shows a peculiar wriggling motion, waves of transverse constriction
passing along the body from end to end, as well as flexures in different
meridians. Such motions are termed "euglenoid." The front part is
colourless, but under a low {125}power the rest of the cell is green, owing
to the numerous chlorophyll bodies or chloroplasts. The outermost layer of
the cytoplasm shows a somewhat spiral longitudinal striation, possibly due
to muscular fibrils. The interior contains many laminated plates of
paramylum, and a large single nucleus. At the front of the body at the base
of the flagellum is a red "eye-spot" on the dorsal side of the pharynx-tube
or pit, from which the flagellum protrudes. Wager has shown that this tube
receives, also on its dorsal side, the opening of a large vacuole,
sometimes called the reservoir, for into it discharges the contractile
vacuole (or vacuoles). The eye-spot is composed of numerous granules,
containing the vegetal colouring matter "haematochrome." It embraces the
lower or posterior side of the communication between the tube and the
reservoir. The flagellum has been traced by Wager through the tube into the
reservoir, branching into two roots where it enters the aperture of
communication, and these are inserted on the wall of the reservoir at the
side opposite the eye-spot. But on one of the roots near the bifurcation is
a dilatation which lies close against the eye-spot, so that it can receive
the light reaction. _Euglena_ is an extremely phototactic organism. It
shows various wrigglings along the longitudinal axis, and transverse waves
of contraction and expansion may pass from pole to pole.[138]
Among the Chrysomonadaceae the genus _Zooxanthella_, Brandt, has already
been described under the Radiolaria (p. 86), in the jelly of which it is
symbiotic. It also occurs in similar union in the marine Ciliates,
_Vorticella sertulariae_ and _Scyphidia scorpaenae_, and in _Millepora_ (p.
261) and many Anthozoa (pp. 373 f., 396).
Of the Chlamydomonadidae, _Sphaerella_ (_Haematococcus_, Ag.) _pluvialis_
(Fig. 43), and _S. nivalis_, in which the green is masked by red pigment,
give rise to the phenomena of "red snow" and "bloody rain." The type genus,
_Chlamydomonas_, is remarkable for the variations from species to species
in the character and behaviour of the gametes. Sometimes they are equal, at
other times of two sizes. In some species they fuse immediately on
approximation, in the naked active state; in others, they encyst on
approaching, and unite by the emission of a fertilising tube, {126}as in
the Algal Conjugatae. _Zoochlorella_ is symbiotic in green Ciliata (pp. 153
f., 158), Sponges (p. 175), _Hydra_ (p. 256), and Turbellaria (Vol. II. p.
43).
[Illustration: FIG. 43.—_Sphaerella pluvialis._ A, motile stage; B, resting
stage; C, D, two modes of fission; E, _Sphaerella lacustris_, motile stage.
_chr_, Chromatophores; _c.vac_, contractile vacuole; _c.w_, cell-wall;
_fl_, flagella; _nu_, nucleus; _nu'_, nucleolus; _pyr_, pyrenoids. (From
Parker's _Biology_.)]