(§§ 201-217.)
201. _Mechanism of the Functions._--The vital phenomena of the Radiolaria
are dependent upon the mechanical functions of their unicellular body, and
like those of all other organisms, are to be referred to physical and
chemical natural laws. All processes which appear in the life of the
Radiolaria are, therefore, ultimately to be explained by the attraction and
repulsion of the smallest particles, which compose the different portions
of their unicellular body; and the sensation of pleasure or the opposite is
in its turn the exciting cause of these elementary movements. Many adaptive
arrangements in the Radiolarian organism may produce the appearance of
being the premeditated result of causes working towards an end
("zweckthätig," _causæ finales_), but as opposed to this deceptive
appearance it must here be expressly stated that these may be recognised in
accordance with the developmental theory as the necessary consequence of
mechanical causes (_causæ efficientes_).
Our _physiological_ acquaintance with the Radiolaria has by no means
progressed so far as our _morphological_, so that the incomplete
communications which are placed here for the sake of completeness must be
regarded merely as preliminary fragments, not as fully elaborated
results. Since my recent investigations have been mainly in the direction
of morphology, I can add but little to the physiological conclusions,
which I stated at length in my monograph twenty-four years ago (L. N. 16,
pp. 127-165). Recently the vegetative physiology of the Radiolaria has
been much advanced by the recognition of the symbiosis with the Xanthellæ
(§ 205, L. N. 22, 39, 42). In addition Karl Brandt has recently (1885)
published several important contributions to the physiology of the
Polycyttaria or Sphaerozoea (L. N. 52).
202. _Distribution of Functions._--The distribution of the functions among
the various parts of the unicellular organism of the Radiolaria corresponds
directly to their anatomical composition, so that physiologically as well
as morphologically the central capsule and the extracapsulum appear as the
two coordinated main components. On the one hand the _central capsule_ with
its endoplasm and enclosed nucleus is the central organ of the "cell-soul"
(Zellseele), the unit regulating its animal and vegetative functions, and
the special organ of reproduction and inheritance. The _extracapsulum_
forms, on the other hand, by its calymma the protective envelope of the
central {cxxix}capsule, the support of the soft pseudopodia and the
substratum of the skeleton; the calymma acts also as a hydrostatic
apparatus, whilst the radiating pseudopodia are of the greatest importance
both as organs of nutrition and adaptation, as well as of motion and
sensation (§ 15). If, however, the vital functions as a whole be divided in
accordance with the usual convention into the two great groups of
_vegetative_ (nutrition and reproduction) and _animal_ (motion and
sensation), then the central capsule would be mainly the organ of
reproduction and sensation, and the extracapsulum the organ of nutrition
and motion.
The numerous separate vital phenomena, which by accurate physiological
investigation may be distinguished in the unicellular Radiolarian
organism, may be distributed in the above indicated conventional fashion
into a few larger and several smaller groups; it must always be borne in
mind, however, that these overlap in many respects, and that the division
of labour among the different organs in these Protista is somewhat
complicated, notwithstanding the apparent simplicity of their unicellular
organization. A general classification of the groups of functions is
difficult, because each individual organ discharges several different
functions. Thus the central capsule is pre-eminently the organ of
reproduction and inheritance, but not less (though less conspicuous) is
its importance as the psychical central organ, the unit regulating the
processes of sensation, motion, and also nutrition. In this last respect
it is comparable to the nerve-centres of the Metazoa, whilst the
peripheral nervous system of the latter (including the organs of sense
and the muscles) are in the present instance represented by the
pseudopodia, which are at the same time the most important organs of
nutrition and adaptation. In the calymma also in similar fashion several
different physiological functions are united.
203. _Metastasis._--The functions of metastasis and nutrition have in all
Radiolaria a purely animal character, so that these Rhizopoda from the
physiological standpoint are to be regarded as truly _unicellular animals_,
or Protozoa ("Urthiere"). Since they do not possess, like plants, the power
of forming synthetically the compounds (protoplasm, carbohydrates, &c.)
necessary for their sustenance, they are compelled to obtain them
ready-formed from other organisms. Like other true animals they evolve
carbon dioxide by the partial oxidation of those products, and hence they
successively take up the oxygen necessary to their existence from their
environment.
The question whether the Radiolaria are to be regarded as true animals I
discussed fully from various points of view in 1862, and finally answered
in the affirmative (L. N. 16, pp. 159-165). Afterwards, when in my
Generelle Morphologie (1866) I sought to establish the kingdom Protista,
I removed the Radiolaria along with the other Rhizopoda from the animal
kingdom proper and placed them in the kingdom Protista (Bd. i. pp.
215-220; Bd. ii. p. xxix). Compare also my Protistenreich (L. N. 32) and
my Natürliche Schöpfungsgeschichte (vii. Aufl., 1879, p. 364). Both these
steps appear fully justified when considered in the light of our present
increased knowledge. From the _physiological_ standpoint the Radiolaria
appear as unicellular _animals_, for in this respect the animal character
of their metastasis (that proper to an oxidising organism) furnishes the
sole {cxxx}criterion. On the other hand, from the morphological
standpoint, they are to be classed as neutral Protista, for in this
respect their unicellular character is the prominent feature, and
distinguishes them from all true multicellular animals (Metazoa). Compare
my Gastræa Theorie (1873, Jena. Zeitschr. für Naturwiss., Bd. viii. pp.
29, 53).
204. _Nutrition._--The nutritive materials which the Radiolaria require for
their sustenance, especially albuminates (plasma) and carbohydrates
(starch, &c.), they obtain partly from foreign organisms which they capture
and digest, and partly directly from the Xanthellæ or Philozoa, the
unicellular Algæ, with which they live in symbiosis (§ 205). _Zooxanthella
intracapsularis_, found in the ACANTHARIA (§ 76), is probably of the same
significance in this respect as _Zooxanthella extracapsularis_ of the
SPUMELLARIA and NASSELLARIA (§ 90); and perhaps the same is true also of
_Phæodella extracapsularis_ (or _Zoochlorella phæodaris_?) of the PHÆODARIA
(§ 89). The considerable quantity of starch or amyloid bodies, elaborated
by these inquiline symbiontes, as well as their protoplasm and nucleus, are
available, on their death, for the nutrition of the Radiolaria which
harbour them. Nutrition by means of other particles obtained by the
pseudopodia from the surrounding medium is by no means excluded; indeed it
may be regarded as certain that numerous Radiolaria (especially such as
contain no symbiotic Algoid cells) are nourished for the most part or
exclusively by this means. Diatoms, Infusoria, Thalamophora (Foraminifera)
as well as decaying particles of animal and vegetable tissues can be seized
directly by the pseudopodia and conveyed either to the sarcodictyum (on the
surface of the calymma) or to the sarcomatrix (on the surface of the
central capsule) in order to undergo digestion there. The indigestible
constituents (siliceous shells of Diatoms and Tintinnoidea, calcareous
shells of small Monothalamia and Polythalamia, &c.) are here collected
often in large numbers and removed by the streaming of the protoplasm.
The inception and digestion of nutriment, as it usually appears to take
place by the pseudopodia, has already been so fully treated in my
Monograph (L. N. 16, pp. 135-140), and since then in my paper on the
sarcode body of the Rhizopoda (L. N. 19, p. 342), that I have nothing of
importance to add. Quite recently Karl Brandt has expressed a doubt as to
whether the taking up of formed particles by the pseudopodia and their
aggregation in the calymma be really connected with the process of
nutrition. He is disposed rather to believe that these foreign bodies are
usually only accidentally and mechanically brought into the calymma, and
that the nourishment of the Radiolaria is derived exclusively or
pre-eminently from the symbiotic Xanthellæ (L. N. 52, pp. 88-93). I must,
however, maintain my former opinion, which I have only modified insomuch
that I now regard the sarcodictyum (on the outer surface of the calymma,
§ 94) rather than the sarcomatrix (on the outer surface of the central
capsule, § 92) as the principal seat of true digestion and assimilation.
From the sarcodictyum the dissolved and assimilated nutritive matters may
pass by the intracalymmar pseudopodia (or sarcoplegma, § 93) into the
sarcomatrix, and hence may reach the endoplasm through the openings in
the central capsule. To what an extent the Radiolaria are capable of
taking up even large formed bodies into the calymma, is shown by the
{cxxxi}striking instance of _Thalassicolla sanguinolenta_, which becomes
so deformed by the inception of numerous coccospheres and coccoliths,
that I described it as a special genus under the name _Myxobrachia_
(compare pp. 23, 30; also L. N. 21, p. 519, Taf. xviii., and L. N. 33, p.
37).
205. _Symbiosis._--Very many Radiolaria, but by no means all members of
this class, live in a definite commensal relation with yellow unicellular
Algæ of the group Xanthellæ. In the ACANTHARIA they live within the central
capsule (_Zooxanthella intracapsularis_, § 76), in the SPUMELLARIA and
NASSELLARIA, on the other hand, within the calymma but outside the central
capsule (_Zooxanthella extracapsularis_, § 90); in the PHÆODARIA a special
form of these symbiotic unicellular Algæ appears to inhabit the phæodium in
the extracapsulum, and to compose a considerable portion of the phæodellæ
(_Zooxanthella phæodaris_, § 90, or better perhaps _Zoochlorella
phæodaris_, § 89). Undoubtedly this commensal life is in very many cases of
the greatest physiological significance for both the symbiontes, for the
animal Radiolarian cells furnish the inquiline Xanthellæ not only with
shelter and protection, but also with carbon dioxide and other products of
decomposition for their nutriment; whilst on the other hand the vegetable
cells of the Xanthellæ yield the Radiolarian host its most important supply
of nutriment, protoplasm and starch, as well as oxygen for respiration.
Hence it is not only theoretically possible, but has been experimentally
proved, that Radiolaria which contain numerous Xanthellæ can exist without
extraneous nutriment for a long period in closed vessels of filtered
sea-water, kept exposed to the sunlight; the two symbiontes furnish each
other mutually with nourishment, and are physiologically supplementary to
each other by reason of the opposite nature of their metastasis. This
symbiosis is not necessary, however, for the existence of the Radiolaria;
for in many species the number of Xanthellæ is very variable and in many
others they are entirely wanting.
The symbiosis of the Radiolaria and Xanthellæ, or "yellow cells" (§§ 76,
90) was first discovered by Cienkowski in 1871 (L. N. 22). Ten years
later this important and often doubted fact was established by extended
observations and experiments almost simultaneously by Karl Brandt (L. N.
38, 39) and Patrick Geddes (L. N. 42, 43). This commensal life may be
compared with that of the lichens, in which an organism with vegetable
metastasis (the Algoid gonidia) and an organism with animal metastasis
(the Fungoid hyphæ) are intimately united for mutual benefit. But the
symbiosis of the Xanthellæ and Radiolaria is not as in the lichens a
phenomenon essential for their development, but has more or less the
character of an accidental association. The number of the inquiline
Xanthellæ is so variable even in one and the same species of Radiolaria,
that they do not appear to be exactly essential to its welfare; and in
many species they are entirely wanting. Their significance is
questionable in the case of those numerous deep-sea Radiolaria which live
in complete darkness, and in which, therefore, the Xanthellæ, even if
present, could excrete no oxygen on account of the want of light.
Nevertheless it is possible that the phæodellæ of the PHÆODARIA (usually
green, olive, or brown in colour), which are true cells, represent
vegetable symbiontes, {cxxxii}which in the absence of sunlight are able
to evolve oxygen by the aid of the phosphoresence of other abyssal
animals. Since the PHÆODARIA are, for the most part, dwellers in the
deep-sea, and since the voluminous phæodium must be of great
physiological importance, a positive solution of this hypothetical
question would be of no small interest (compare § 89).
206. _Respiration._--The respiration of the Radiolaria is animal in nature,
since all Protista of this class, like all other true Rhizopoda, take in
oxygen and give off carbon dioxide. Probably this process goes on
continuously and is tolerably active, as may be inferred from the fact that
Radiolaria cannot be kept for long in small vessels of sea-water unless
either they contain numerous Xanthellæ or the water is well aërated. The
oxygen is obtained from two sources, either from the surrounding water or
from the enclosed Xanthellæ, which in sunlight evolve considerable
quantities of this gas. Correspondingly, the carbon dioxide which is formed
during the process of oxidation of the Radiolaria is either given up to the
surrounding water or to the inquiline Xanthellæ, which utilise it for their
own sustenance (§§ 204, 205).
The significance of the symbiotic Xanthellæ for the respiration of the
enclosing Radiolaria may be shown experimentally in the following way. If
two Polycyttarian colonies of equal size, both of which contain numerous
Xanthellæ, be placed in equal quantities of filtered sea-water in sealed
glass tubes, and if one tube be placed in the dark the other in the
light, the colony in the former rapidly perishes, but not that in the
latter; the Xanthellæ excrete only under the influence of sunlight the
oxygen necessary for the life of the Radiolarian (compare Patrick Geddes,
L. N. 42, p. 304).
207. _Circulation._--In the protoplasm of all Radiolaria, both inside and
outside the central capsule, slow currents may be recognised which fall
under the general term circulation, and have already been compared to the
cyclosis in the interior of animal and vegetable cells, as well as to the
sarcode streams in the body of other Rhizopoda. These plasmatic currents or
"plasmorrheumata" probably continue throughout the whole life of the
Radiolaria, and are of fundamental importance for the performance of their
vital functions. They depend upon slow displacements of the molecules of
the plasma (plastidules or micellæ) and cause a uniform distribution of the
absorbed nutriment and a certain equalisation of the metastasis.
Furthermore they are of great importance also in the inception of
nutriment, the formation of the skeleton, locomotion, &c. Sometimes the
circulation is directly perceptible in the plasma itself; but usually it is
only visible owing to the presence of granules (sarcogranula), which are
suspended in the plasma in larger or smaller numbers. The movements of
these granules are usually regarded as passive, due to the active
displacement of the molecules of the plasma. Although the intracapsular
protoplasm is in communication with the extracapsular through the openings
in the capsule membrane, nevertheless the currents exhibit certain
differences {cxxxiii}in the two portions of the malacoma. It is sometimes
possible, however, to recognise the direct connection between them and to
observe how the granules pass through the openings in the capsule-membrane.
208. _Currents in the Endoplasm._--Intracapsular circulation or a certain
slow flowing of the plasma within the central capsule is probably just as
common in the Radiolaria as without it, but it is not so easy to observe in
the former case as in the latter. A more satisfactory proof of these
endoplasmatic currents is furnished by the arrangement of the protoplasm
within the central capsule, since this is (at all events in part) an effect
produced by them. In this respect the two main divisions of the class show
characteristic differences. In the Porulosa (the SPUMELLARIA, § 77, and the
ACANTHARIA, § 78) the endoplasm is in general distinguished by a more or
less distinct radial structure, which is to be regarded as the effect of
alternating centripetal and centrifugal radial streams. In the Osculosa, on
the other hand, this radial structure is absent and the intracapsular
plasmatic streams converge or diverge towards the osculum or main-opening
in the central capsule which lies at the basal pole of its main axis, and
through which the mass of the endoplasm issues into the calymma. The two
legions of the Osculosa, however, present differences in this respect. In
the NASSELLARIA (§ 79) the endoplasmatic currents appear to unite in an
axial main stream at the apex of the monaxon central capsule, and this
apical stream seems to split into a conical bundle, the individual threads
of which pass diverging between the myophane fibrillæ of the podoconus
towards the basis of the central capsule, and issue through the pores of
the porochora. In the PHÆODARIA (§ 80), on the other hand, meridional
currents of endoplasm are probably present on the inner surface of the
capsule, which flow from the aboral pole of the vertical main axis to its
basal pole, and return in the reverse direction.
209. _Currents in the Exoplasm._--Extracapsular circulation, or a distinct
flowing of the plasma outside the central capsule, may be readily observed
in all Radiolaria which are examined alive; this is most readily seen in
the astropodia, or those free pseudopodia which radiate from the
sarcodictyum on the surface of the calymma into the surrounding water. The
granular movement is often quite as clear in the sarcodictyum itself, and
may be recognised in the collopodia, which compose the irregular plasmatic
network within the calymma. More rarely it is possible to follow the
granular stream thence through the sarcomatrix, and further into the
interior of the central capsule. In general the direction of the
extracapsular protoplasmic streams is radial, and it is frequently
possible, even in a single free astropodium, to observe two streams
opposite in direction, the granules on one side of the radial sarcode
thread moving centripetally, those on the other side centrifugally. If the
threads branch, and neighbouring ones {cxxxiv}become united by connecting
threads, the circulation of the granules may proceed quite irregularly in
the network thus formed. The rapidity and character of the extracapsular
currents are subject to great variations.
The different forms of extracapsular sarcode currents have been already
very fully described in my Monograph (L. N. 16, pp. 89-126), and in my
critical essay on the sarcode body of the Rhizopoda (L. N. 19, p. 357,
Taf. XXVI.).
210. _Secretion._--Under the name _secretions_, in the strict sense, all
the skeletal formations of the Radiolaria may be included. They may be
divided according to their chemical composition into three different
groups: pure silica in the SPUMELLARIA and NASSELLARIA, a silicate of
carbon in the PHÆODARIA, and acanthin in the ACANTHARIA (compare § 102). It
may indeed be assumed that these skeletons arise directly by a chemical
metamorphosis (silicification, acanthinosis, &c.) of the pseudopodia and
protoplasmic network; and this view seems especially justified in the case
of the Astroid skeleton of the ACANTHARIA (§ 114), the Spongoid skeleton of
the SPUMELLARIA (§ 126), the Plectoid skeleton of the NASSELLARIA (§ 125),
the Cannoid skeleton of the PHÆODARIA (§ 127), and several other types. On
closer investigation, however, it appears yet more probable that the
skeleton does not arise by direct chemical metamorphosis of the protoplasm,
but by secretion from it; for when the dissolved skeletal material (silica,
acanthin) passes from the fluid into the solid state, it does not appear as
imbedded in the plasma, but as deposited from it. However, it must be borne
in mind that a hard line of demarcation can scarcely, if at all, be drawn
between these two processes. In the ACANTHARIA the intracapsular sarcode is
the original organ of secretion of the skeleton; in the other three
legions, on the other hand, the extracapsulum performs this function (§§
106, 107). In addition to the skeleton, we may regard as secretions (or
excretions) the intracapsular crystals (§ 75) and concretions (§ 75A), and
perhaps certain pigment-bodies (§§ 74, 88); and further, the calymma (§ 82)
may be considered to be a gelatinous secretion of the central capsule, and
perhaps also the capsule-membrane, in so far as it represents only a
secondary excretory product of the unicellular organism.
211. _Adaptation._--The innumerable and very various adaptive phenomena
which we meet with in the morphology of the Radiolaria, and especially in
that of their skeleton, are like other phenomena of the same kind, to be
ultimately referred to altered nutritional relations. These may be caused
directly either by the influence of external conditions of existence
(nutrition, light, temperature, &c.), or by the proper activity of the
unicellular organism (use or disuse of its organs, &c.), or, finally, by
the combined action of both causes in the struggle for existence. In very
many cases the cause to which the origin of a particular form of Radiolaria
is due may be directly perceived or at least guessed at with considerable
probability; thus, for example, the lattice-shells {cxxxv}may be explained
as protective coverings, the radial spines as defensive weapons, and the
anchor-hooks and spathillæ as organs of prehension, which are of advantage
to their possessors in the struggle for existence; the regular arrangement
of the radial spines in the Radiolaria may also be explained on hydrostatic
grounds, it being advantageous that the body should be maintained in a
definite position of equilibrium, &c. The well-known laws of _direct_ or
_actual adaptation_, which we designate cumulative, correlative, divergent
adaptation, &c., here explain a multitude of morphological phenomena. The
connection is less distinct in the case of the laws of _indirect_ or
_potential adaptation_, although this must play as important a part in the
formation of the Radiolaria as in that of other organisms (compare on this
head my Generelle Morphologie, Bd. ii. pp. 202-222).
212. _Reproduction._--The most common form of reproduction in the
Radiolaria is the formation of spores in the central capsule, which in this
respect is to be regarded as a sporangium (§ 215). In many Radiolaria
(Polycyttaria and PHÆODARIA), however, there occurs in addition an increase
of the unicellular organism by simple division (§ 213); upon this the
formation of colonies in the social Radiolaria is dependent (§ 14).
Reproduction by gemmation is much less common, and has hitherto been
observed only in the Polycyttaria (§ 214). In this group alone there also
occur at certain times two different forms of swarm-spores which copulate,
and thus indicate the commencement of sexual reproduction (Alternation of
Generations, § 216). The general organ of reproduction is in all cases the
central capsule, whilst the extracapsulum never takes an active part in the
process.
213. _Cell-Division._--Increase by cell-division among the Radiolaria in
the early stage, before the formation of the skeleton, is widely
distributed (perhaps even general?); in the adults of this class it is
rather rare and limited to certain groups. It is most readily observed in
the Polycyttaria; the growth of the colonies in this social group depends
mainly (and in many species exclusively) upon repeated spontaneous division
of the central capsule; all the individuals of each colony (in so far as
this has not arisen by the accidental fusion of two or more colonies) are
descendants of a single central capsule, which has arisen from an asexual
swarm-spore (§ 215) or from the copulation of two sexual swarm-spores (§
216). Whilst the central capsules of the colonies continually increase by
division, their calymma remains a common gelatinous sheath. Among the
SPUMELLARIA reproduction by simple cell-division probably occurs also in
many monozootic #Collodaria#. Among the ACANTHARIA the peculiar group
Litholophida has perhaps arisen by the spontaneous division of
#Acanthonida# (see p. 734). Among the PHÆODARIA increase by cell-division
seems to occur commonly in many groups, as in the #Phæocystina#, which have
no skeleton (Phæodinida, Pl. 101, {cxxxvi}fig. 2), or only an incomplete
Beloid skeleton (Cannorrhaphida, Pl. 101, figs. 3, 6, and Aulacanthida, Pl.
104, figs. 1-3). The #Phæosphæria# also (Aulosphærida, Coelacanthida) and
the #Phæogromia# (Tuscarorida, Challengerida) appear sometimes to divide;
at all events, their central capsule often contains two nuclei. Of special
interest is the spontaneous division of the #Phæoconchia#, especially the
Concharida (Pl. 124, fig. 6). In all monozootic Radiolaria, the nucleus
first divides by a median constriction into two equal halves (usually by
the mode of direct division); then the central capsule becomes constricted
in the middle (in the PHÆODARIA in the vertical main axis), and each
portion of the capsule retains its own nucleus. In the #Phæoconchia# each
half or daughter-cell corresponds to one valve of the shell, dorsal or
ventral, so that probably on subsequent separation each daughter-cell
retains one valve of the mother-cell, and forms a new one for itself by
regeneration (as in the Diatoms). In the polyzootic Radiolaria, which
already contain many small nuclei, but usually only a single central
oil-globule in each central capsule, the division of the latter is preceded
by that of the oil-globule. In many Polycyttaria the colony as a whole
multiplies by division.
The increase of the central capsule by division was first described in
1862 in my Monograph (L. N. 16, p. 146); since then R. Hertwig (L. N. 26,
p. 24) and K. Brandt (L. N. 52, p. 144) have confirmed my statement. In
the PHÆODARIA the division of the central capsule appears always to take
place in the main axis; in the bilateral sometimes in the sagittal,
sometimes in the frontal plane. In the Tripylea each daughter-cell seems
to retain one parapyle and half the astropyle (compare the general
description of the PHÆODARIA, Pl. 101, figs. 1-6, Pl. 104, figs. 1-3, and
also Hertwig, L. N. 33, p. 100, Taf. x. figs. 2, 11). Regarding the
spontaneous division of colonies of the Polycyttaria, see K. Brandt, L.
N. 52, p. 142.
214. _Cell-Gemmation._--Reproduction by gemmation has hitherto been
observed only in the social Radiolaria, but in them it appears to be widely
distributed, and in very young colonies is perhaps almost universally
present. The gemmules or capsular buds (hitherto described as
"extracapsular bodies") are developed on the surface of young central
capsules before these had secreted a membrane. They grow usually in
considerable numbers, from the surface of the central capsule, which is
sometimes quite covered with them. Each bud usually contains a
raspberry-like bunch of shining fatty globules, and by means of reagents a
few larger or a considerable number of smaller nuclei may be recognised in
them; the naked protoplasmic body of the bud is not enclosed by any
membrane. As soon as the buds have reached a certain size they are
constricted off from the central capsule and separated from it, being
distributed in the meshes of the sarcoplegma by the currents in the
exoplasm. Afterwards each bud becomes developed into a complete central
capsule by surrounding itself with a membrane when it has attained a
definite size. From the special relations of the process of nuclear
formation, which take place in the multiplication of the {cxxxvii}social
central capsules by gemmation and by cell-division, it would appear that
the capsules produced by the former method afterwards produce anisospores,
whilst those in the latter way yield isospores (§ 216).
The gemmules or capsular buds of the Polycyttaria were first accurately
described by Richard Hertwig (L. N. 26, pp. 37-39), under the name
"extracapsular bodies," and their significance rightly indicated; earlier
observers had incidentally mentioned and figured them, but had not seen
their origin from the central capsule. Quite recently Karl Brandt has
given a very painstaking account of them in the different Polycyttarian
genera (L. N. 52, pp. 179-198). In the Monocyttaria such a formation of
buds has not yet been observed. The basal lobes of the central capsule,
which occur in many NASSELLARIA, are not buds, but simple processes of
the capsule, due to its protrusion through the collar pores of the
cortinar septum (§ 55).
215. _Sporification._--Asexual reproduction by the formation of movable
flagellate spores has been hitherto observed only in a very small number of
genera; but since these belong to very different groups, and since the
comparative morphology of the capsule appears to be similar throughout as
regards the structure and development of its contents, it may be safely
assumed that this kind of reproduction occurs quite generally in the
Radiolaria. In all cases it is the contents of the central capsule, from
which the swarm-spores are formed, both nucleus and endoplasm taking an
equal share in the process; in all cases the spores produced are very
numerous, small, ovoid or reniform, and have one or two very long slender
flagella at one extremity (see §§ 141, 142). Since the whole contents of
the mature central capsule are used up in the formation of these flagellate
zoospores, it discharges the function of a sporangium. The division of the
simple primary nucleus into numerous small nuclei, which usually
(serotinous Radiolaria) takes place only shortly before sporification, but
sometimes (precocious Radiolaria, § 63) happens very early, is the
commencement of the often repeated process of nuclear division, which
terminates with the production of a very large number of small
spore-nuclei. The nucleolus often divides very peculiarly (§ 69, C). Each
spore nucleus becomes surrounded by a portion of endoplasm and usually
receives in addition one or more fatty granules, and sometimes also a small
crystal (hence the "crystal-spores"). The size of the flagellate zoospores
which emerge from the ruptured central capsule and swim freely in the water
by means of their flagellum, varies generally between 0.004 and 0.008 mm.
The extracapsulum is not directly concerned in the sporification, but
undergoes degeneration during the process and perishes at its conclusion.
The first complete and detailed observations on the formation of spores
in the Radiolaria were published by Cienkowski in 1871 and related to two
genera of Polycyttaria, the skeletonless _Collozoum_ and the
spherical-shelled _Collosphæra_ (L. N. 22, p. 372, Taf. xxix.). These
were subsequently continued and supplemented by R. Hertwig (1876, L. N.
26, pp. 26-42, and L. N. 33, p. 129), and a general summary of these
results has been given by Bütschli (L. N. 41, pp. 449-455).
{cxxxviii}Recently Karl Brandt has given a very detailed and fully
illustrated account of the sporification of the Polycyttaria (L. N. 52,
pp. 145-178). I have also had the opportunity during my sojourn in the
Canary Islands (1866), in the Mediterranean at Corfu (1877), and
Portofino (1880), as well as in Ceylon (1881), of observing the
development of flagellate zoospores from the central capsule of
individuals of all four legions: among the SPUMELLARIA in certain
#Colloidea#, #Beloidea#, #Sphæroidea#, and #Discoidea#, among the
ACANTHARIA in several #Acanthometra# and #Acanthophracta#, among the
NASSELLARIA in individuals belonging to the #Stephoidea#, #Plectoidea#,
and #Cyrtoidea#, and among the PHÆODARIA in one Castanellid. In most
zoospores I could distinctly observe only a single long flagellum;
sometimes, however, two or even three appeared to be present, but the
determination of their number is very difficult.
216. _Alternation of Generations._--A peculiar form of reproduction, which
may be designated "alternation of generations," appears to occur generally
in the Polycyttaria, but has not yet been observed in the Monocyttaria. All
#Collozoida#, #Sphærozoida#, and Collosphærida which have hitherto been
carefully and completely examined with respect to their development, are
distinguished by the production of two different kinds of swarm-spores,
isospores and anisospores. The _Isospores_ (or monogonous spores)
correspond to the ordinary asexual zoospores of the Monocyttaria (§ 215);
they possess a homogeneous, doubly refracting nucleus of uniform
constitution and develop asexually, without copulation. The _Anisospores_
(or amphigonous spores), on the other hand, are sexually differentiated and
possess a heterogeneous, singly refracting nucleus of twofold constitution;
they may therefore be distinguished as female macrospores and male
microspores. The _Macrospores_ (or gynospores, comparable with the female
macrogonidia of many Cryptogams) are larger, less numerous, and possess
larger nuclei, which are less easily stained, and have a fine filiform
trabecular network. On the other hand the _Microspores_ (or _androspores_,
comparable with the male microgonidia) are much smaller and more numerous,
and are distinguished by their smaller nuclei, which have thicker tuberculæ
and become stained more intensely. The gynospores and androspores are
developed in the #Collozoida# and #Sphærozoida# in the same individual, but
not in the Collosphærida. It is very probable that these two forms of
anisospores copulate with each other after their exit from the central
capsule and thus produce a new cell by the simplest mode of sexual
reproduction. But, since the same Polycyttaria, which produce these
anisospores, at other times give rise to ordinary or asexual isospores, it
is further possible that these two forms of reproduction alternate with
each other, and that the Polycyttaria thus pass through a true alternation
of generations. This has not yet been observed in the Monocyttaria, and
hence these latter seem to bear to the Polycyttaria a relation similar to
that in which the sexless solitary Flagellata (Astasiea) stand to the
sexual social Flagellata (Volvocinea). In the two analogous cases the
sexual differentiation may be regarded as a consequence of the social life
in the gelatinous colonies.
{cxxxix}The _sexual differentiation of the Polycyttaria_ was first
discovered in 1875 by R. Hertwig, and accurately described in the case of
_Collozoum inerme_ as occurring in addition to the formation of the
ordinary crystal-spores (L. N. 26, p. 36); compare also the general
discussion of Bütschli (L. N. 41, p. 52). Recently Karl Brandt has
demonstrated the formation of both homogeneous isospores (crystal-spores)
and heterogeneous anisospores (macro- and microspores) in seven different
species of Polycyttaria, and has come to the conclusion that in all
social Radiolaria there is a regular alternation between the former and
latter generations. Compare his elaborate account of the colonial
Radiolaria of the Gulf of Naples (L. N. 52, pp. 145-178).
217. _Inheritance._--Inheritance is to be regarded as the most important
accompaniment to the function of reproduction, and especially in the
present case, because the comparative morphology of the Radiolaria
furnishes abundant instances of the action of its different laws. The laws
of _conservative inheritance_ are illustrated by the comparative anatomy of
the larger groups; thus, in the four legions the characteristic
peculiarities of the central capsule are maintained unaltered in
consequence of continuous inheritance, although great varieties appear in
the skeleton in each legion. The individual parts of the skeleton furnish
by their development on the one hand and their degeneration on the other,
especially in the smaller groups, examples of _progressive inheritance_.
Thus in the SPUMELLARIA the constant formation of the primary lattice-shell
(a central medullary shell) and its ontogenetic relation to the secondary
one, which is developed concentrically round it, can only be explained
phylogenetically by conservative inheritance, whilst on the other hand the
characteristic differentiation of the axes in the various families of
SPUMELLARIA is to be explained by progressive inheritance. In the
ACANTHARIA the arrangement of the twenty radial spines (in accordance with
Müller's law, §§ 110, 172) was first acquired by a group of the most
archaic #Actinelida# (Adelacantha) through hydrostatic adaptation, and has
since been transmitted by inheritance to all the other families of the
legion (Icosacantha). The morphology of the NASSELLARIA is not less
interesting, because here several different heritable elements (the primary
sagittal ring and the basal tripod) combine in the most manifold ways in
the formation of the skeleton (compare §§ 123, 124, 182). The affinities of
the genera in the different families yield an astonishing variety of
interesting morphological phenomena, which can only be explained by
progressive inheritance. The same is true also of the PHÆODARIA. In this
legion the primary inheritance is especially manifested in the constant and
firm structure of the central capsule with its characteristic double wall
and astropyle, whilst the formation of the skeleton in this legion proceeds
in different directions by means of divergent adaptation. The morphology of
the Radiolaria thus proves itself a rich source of materials for the
physiological study of adaptation and inheritance.
{cxl}CHAPTER VIII.--ANIMAL FUNCTIONS.
(§§ 218-225.)
218. _Motion._--In addition to the internal movements which appear
generally in the unicellular Radiolaria and have already been mentioned as
plasmatic currents in treating of the circulation (§§ 207-209), two
different groups of external motor phenomena are to be observed in this
class: first, the _contraction_ of individual parts, which brings about
modifications of form (§ 220), and secondly, voluntary or reflex
_locomotion_ of the whole body (§ 220). These movements are partly due to
changes in form of undifferentiated plasmatic threads or sarcode filaments,
partly to the actual contraction of differentiated filaments which are
comparable to muscle fibrillæ, and must therefore be distinguished as
myophanes. In addition to this, endosmose and exosmose probably play an
important part in some of the locomotive phenomena, but nothing is yet
certainly known regarding these osmotic processes. We are at present
equally ignorant whether all the movements of the Radiolaria are simply
reflex (direct consequences of irritation) or whether they are in part
truly spontaneous.
219. _Suspension._--From direct observation of living Radiolaria, as well
as from deductive reasoning, based upon their morphology (and especially
their promorphology, §§ 17-50), the conclusion appears justified that all
Protista of this class in their normal condition float suspended in the
sea-water, either at the surface or at a definite depth. A necessary
condition of this hydrostatic suspension is that the specific gravity of
the Radiolarian organism must be equal to, or but slightly greater than
that of sea-water. The increase in specific gravity brought about by the
production of the siliceous skeleton, is compensated by the lighter fatty
globules, and partly perhaps by the calymma, especially when the latter
contains vacuoles or alveoles. The fluid or jelly contained in the latter
appears to be for the most part lighter than sea-water (containing no salt,
or only a very small quantity?). But if the specific gravity of the whole
body should be generally (or perhaps always) slightly greater than that of
sea-water, then the organism would be prevented from sinking, partly by the
increased friction, due to the radiating pseudopodia and the radial spines
usually present, and partly perhaps by active (if only feeble) movements of
the pseudopodia.
220. _Locomotion._--Active locomotion of the whole body, which is very
probably to be regarded as voluntary, occurs in the Radiolaria in three
different modes; (1) the vibratile movement of the flagellate swarm-spores;
(2) the swimming of the floating organisms; (3) the slow creeping of those
which rest accidentally upon the bottom. {cxli}The _vibratile_ movement of
the swarm-spores is the result of active sinuous oscillation of the single
or multiple flagellum, and is not essentially different from that of
ordinary flagellate Infusoria (see note A). Of the active swimming of
mature Radiolaria, only that form is known which is vertical in direction
and causes the sinking and rising in the sea-water. This is probably, for
the most part (perhaps exclusively), due to increase or diminution in the
specific gravity, which is perhaps brought about by the retraction or
protrusion of the pseudopodia; slow, oscillating, sinuous motions of these
organs have been directly observed to take place (though very slowly) in
suspended living Radiolaria. The most important hydrostatic organ is
probably the calymma, by the contraction of which the specific gravity is
increased, while it is diminished by its expansion; the contraction is
probably brought about by active contraction of the sarcodictyum, and is
connected with exosmosis, while the expansion is probably due to the
elasticity of the calymma and the inception of water by endosmosis. In the
#Acanthometra# (§ 96) the peculiar myophriscs appear to be charged with the
duty of distending the gelatinous envelope, and thus diminishing the
specific gravity; the latter increases again when the myophriscs are
relaxed, and the calymma contracts by virtue of its own elasticity (see
note B). The slow _creeping locomotion_ exhibited by Radiolaria on a glass
slide under the microscope, does not differ from that of the Thalamophora
(Monothalamia and Polythalamia), but can only occur normally when the
animal accidentally comes into contact with a solid surface or sinks to the
bottom of the sea. Whether this actually occurs periodically is not known
(see note C). The slow or gliding locomotion exhibited by creeping Monozoa
on a glass slide is due to muscle-like contractions of bundles of
pseudopodia, just as in the case of the social central capsules of Polyzoa,
which live together in the same coenobium and are able to move within their
common calymma sometimes centrifugally to its surface, sometimes towards
the centre where they aggregate into a roundish mass (see note D).
A. Regarding the movement of the flagella in mature swarm-spores compare
L. N. 22, p. 375; L. N. 26, pp. 31, 35; L. N. 41, p. 452, and L. N. 52,
p. 170.
B. On the active vertical swimming movements of mature Radiolaria,
especially the cause of sinking and rising, see L. N. 16, p. 134; L. N.
41, p. 443, and L. N. 52, pp. 97-102.
C. On the active horizontal creeping movements of mature Radiolaria on a
firm ground, compare L. N. 12, p. 10, and L. N. 16, pp. 132-134.
D. Regarding the motion of social central capsules within the same
coenobium and the changes thus brought about in the structure of the
calymma, see L. N. 16, pp. 119-127, and L. N. 52, pp. 75-82.
221. _Contraction._--Motions, which are due to the contraction of
individual portions and cause changes in volume or form, have been partly
already spoken of under the head of locomotion (§ 220) and are partly
connected with other functions. Examples may be seen in the contraction of
the central capsule and of the calymma. A certain {cxlii}contraction of the
central capsule is probably brought about by the myophanes, which arise by
differentiation of the endoplasm and hence may assume different forms in
the four legions. In the SPUMELLARIA, where numerous radial fibrillæ run
from the central nucleus to the capsule membrane (§ 77), the endoplasm is
probably driven out evenly through all the pores of the capsule membrane by
their simultaneous contraction, and hence the volume of the capsule is
diminished in all directions. The ACANTHARIA probably behave similarly,
but are different, inasmuch as the number of their contractile radial
fibrillæ is less, and special axial threads (§ 78) are already
differentiated. In the NASSELLARIA it is probable that owing to the
contraction of the divergent myophane fibrillæ in the podoconus the
vertical axis of the latter is shortened, the opercular rods of the
porochora are lifted, and the endoplasm driven out of its pores, so that
the volume of the monaxon central capsule is diminished (§ 79). In the
PHÆODARIA the same result is probably brought about by the contraction of
the cortical myophane fibrillæ, which run meridionally along the inside of
the capsule membrane from the apical to the basal pole of the vertical main
axis, where they are inserted into the periphery of the astropyle; since
the volume of the capsule is diminished by their contraction (their
spheroidal figure becoming more nearly spherical) the endoplasm will be
driven out through the proboscis of the astropyle. Whilst these
contractions of the central capsule are largely due to differentiated
muscle-like threads of endoplasm (myophanes), this appears to be but rarely
the case with the contractions of the extracapsulum (_e.g._, the myophriscs
of the #Acanthometra#, § 96). Most of the phenomena of contraction which
can be observed in the calymma and pseudopodia depend upon exoplasmatic
currents (§ 209).
222. _Protection._--Of the utmost importance, both for the physiology and
for the morphology of the Radiolaria are their manifold protective
functions, which we now consider under the heading "protection." From the
physiological point of view the consideration of the exposed situation in
which the delicate, free-swimming Radiolarian organism lives, and the
numerous dangers which beset it in the struggle for existence, would lead
_a priori_ to the expectation, that many special protective adaptations
would be developed by natural selection. On the other hand, morphological
experience shows us that this latter has been in action for immeasurable
periods, and has gradually produced an abundance of the most remarkable
protective modifications. Examples of these may be found in the formation
of the voluminous calymma, as a gelatinous protective covering for the
central capsule, and further, the formation of the capsule membrane itself,
which separates the generative contents of the central capsule from the
nutritive exoplasm. The phosphorescence of the central capsule, too (§
223), may be regarded as a useful protective arrangement; as also the
radiating of the numerous pseudopodia in all directions from the surface of
the calymma; for they are of great significance to the {cxliii}well-being
of the organism, both as sensory organs and as prehensile organs. By far
the most important and most varied means for the actual defence of the soft
body is to be seen in the endless modifications of the skeleton; first, in
the production of the enclosing lattice-shells and projecting radial
spines, but especially also in the very varied structure of the individual
parts of the skeleton, and in the special differentiation of the small
appendicular organs which grow out from it (hairs, thorns, spines, scales,
spathillæ, anchors, &c.). Finally "mimicry" possesses a considerable
significance among the different forms of adaptation which are to be
observed in this class.
223. _Phosphorescence._--Many Radiolarians shine in the dark, and their
phosphorescence presents the same phenomena as that of other luminous
marine organisms; it is increased by mechanical and chemical irritation, or
renewed if already extinguished. The light is sometimes greenish, sometimes
yellowish, and appears generally (if not always) to radiate from the
intracapsular fatty spheres (§ 73). Thus these latter unite several
functions, inasmuch as they serve, firstly, as reserve stores of nutriment,
secondly, as hydrostatic apparatus, and thirdly, as luminous organs for the
protection of the Radiolaria; probably the light acts by frightening other
animals, for the phosphorescent animals are provided with spines,
nettle-cells, poison glands or other defensive weapons. The production of
the light depends probably, as in other phosphorescent organisms, upon the
slow oxidation of the fat-globules, which combine with active oxygen in the
presence of alkalis. Phosphorescence is very likely widely distributed
among the Radiolaria.
The shining of the Radiolaria in the dark has been noticed by the
earliest observers of the class (see L. N. 1, p. 163, L. N. 16, p. 2, and
L. N. 52, pp. 136-139). In the winter of 1859 I observed the production
of light in the case of many monozootic and polyzootic Radiolaria, but
inadvertently omitted to record the fact in my Monograph. I made more
accurate observations in the winter of 1866 at Lanzerote in the Canary
Islands, and convinced myself the the light emanates from the central
capsule, and in particular from the fat-globules contained in it. In most
Polycyttaria (both #Collosphærida# and #Sphærozoida#), when each central
capsule contains a large central oil-globule the light radiates from it.
In _Collozoum serpentinum_ (Pl. 3, figs. 2, 3) each cylindrical central
capsule contains a row of luminous spherules like a string of beads. In
_Alacorys friderici_ (Pl. 65, fig. 1) the four-lobed central capsule
contains four shining points. Karl Brandt has recently made more detailed
communication on this point (L. N. 52, p. 137).
224. _Sensation._--The general irritability which we ascribe to all
organisms, and as the basis of which we regard the protoplasm, remains at
an inferior stage of development in the Radiolaria. For although they are
subject to various stimuli, and certainly possess a power of
discrimination, special sensory organs are not differentiated; the
peripheral portions of the protoplasm, and especially the pseudopodia,
rather act both as organs of the different kinds of sensation and various
modes of motion. That different Radiolaria have attained different degrees
of development in this respect may be seen {cxliv}partly by direct
observation of the reaction of the living organism towards various stimuli,
and partly by the comparison of the different conditions of existence under
which Radiolarians exist, both in the most various depths of the ocean and
in all climatic zones (see note A). In general the Radiolaria seem to be
sensitive to the following stimuli; (1) pressure (see note B); (2)
temperature (see note C); (3) light (see note D); (4) chemical composition
of the sea-water (see note E). The reaction towards these stimuli,
corresponding to the sensation of pleasure or dislike which they call
forth, is shown in various forms of motion of the protoplasm, changes in
the currents in it, contraction of the central capsule, changes in the
size, position, and form of the pseudopodia, changes in the volume of the
calymma (by the evocation of water), &c. Among the sensory functions of the
Radiolaria must be especially mentioned their remarkably developed
perception of hydrostatic equilibrium (see note F), as well as their
perception of distances, so clearly shown in the production of equal
lattice-meshes and other regularly formed skeletal structures (see note G).
A. I can add but little to the communication which I made twenty-four
years ago regarding sensation in the Radiolaria (L. N. 16, pp. 128-131).
The most important point would be the great difference in irritability
which must obtain between the pelagic, zonarial and abyssal Radiolaria,
which may be assumed from a consideration of their very different
conditions of existence as regards pressure, light, warmth, nutrition,
&c. It is natural to suppose that the numerous abyssal Radiolaria,
discovered by the Challenger, which live at great depths (2000 to 4500
fathoms) in complete darkness, in icy cold and under an enormous
pressure, must have quite different sensations of pleasure from their
pelagic relatives which live at the surface of the sea under an
equatorial sun. Karl Brandt has recently added much to our knowledge
regarding the special action of different vital conditions upon the
various Polycyttaria and the degrees of their irritability (L. N. 52, pp.
113-132).
B. Regarding the sensation of pressure or sensation of touch of the
Radiolaria and the various degrees of their mechanical irritability, see
L. N. 16, p. 129; L. N. 41, p. 464.
C. Regarding the sensation of warmth or temperature-sense and its
dependence upon different climatic relations, see L. N. 16, p. 129; L. N.
52, pp. 114-129.
D. Regarding the sensation of light, compare L. N. 16, p. 128; L. N. 42,
p. 304; L. N. 52, pp. 102-104, 114.
E. Regarding the sense of taste of the Radiolaria or their peculiar
sensitiveness towards the different chemical composition of the water,
change in its salinity, presence of organic impurities, &c., see L. N.
16, p. 130; L. N. 52, pp. 103, 113. This chemical irritability seems to
be the most highly developed sense in the Radiolaria, even more so than
their mechanical irritability.
F. The perception of hydrostatic equilibrium among the Radiolaria is
immediately visible from the position which their bodies, floating freely
in the water, assume spontaneously, and from the symmetrical development
of the skeleton, which by its gravitation necessitates a definite
position. It may be assumed that the development of the various
geometrical ground forms which correspond to a definite position of
equilibrium, is the result of this particular kind of perception (compare
§§ 40-45).
{cxlv}G. The plastic perception of distance of the pseudopodia is shown
by the symmetry with which the forms composing the regular skeletal
structures (_e.g._, the ordinary lattice-spheres with regular hexagonal
meshes, the radial spines with equidistant branches) are excreted from
the exoplasm. Both this form of sensation and the one first mentioned
(note F) have hitherto received scarcely any attention, but are deserving
of a thorough physiological investigation.
225. _The Cell-Soul (Zellseele)._--The common central vital principle,
commonly called the "soul," which is considered to be the regulator of all
vital functions, appears in the Radiolaria as in other Protista in its
simplest form, as the cell-soul. By the continual activity of this central
"psyche" all vital functions are maintained in unbroken action, and in
uniform correlation. It is also probable that by it the stimulations which
the peripheral portions of the cell receive from the outer world are first
transmitted into true sensation, and that, on the other hand, the volition,
which alone calls forth spontaneous movements, proceeds from it. The
central capsule is most likely the sole organ of this cell-soul or central
psychic organ, and the active portion may be either the endoplasm or the
nucleus, or both. The central capsule may thus (apart from its function as
a sporangium, § 215) be regarded as a simple ganglion cell, physiologically
comparable to the nervous centre of the higher animals, whilst the exoplasm
(sarcomatrix and pseudopodia) are to be compared to the peripheral nervous
system and sense organs of the latter. The great simplicity of the
functions of the cell-soul which appear in the Radiolaria, and the intimate
connection of their different psychic activities, give to these unicellular
Protista a special significance for the comprehension of the monistic
elements of a natural psychology.
Regarding the theory of the cell-soul as the only psychological theory
which is able to explain naturally the true nature of the life of the
soul in all organisms as well as in man, see my address on cell-souls and
soul-cells ("Zellseelen und Seelenzellen") in Gesammelte populäre
Vorträge aus dem Gebiete der Entwickelungslehre, Heft 1, p. 143; Bonn,
1878.
{cxlvi}CHOROLOGICAL SECTION.
----