MUTUALISTS.
In this chapter we bring together animals which live on each other,
without being either parasites or messmates; many of them are towed
along by others; some render each other mutual services, others again
take advantage of some assistance which their companions can give
them; some afford each other an asylum, and some are found which have
sympathetic bonds which always draw them together. They are usually
confounded with parasites or messmates.
Many insects shelter themselves in the fur of the mammalia, or in the
down of birds, and remove from the hair and the feathers the pellicle
and epidermal _débris_ which encumber them. At the same time they
minister to the outward appearance of their host, and are of great
utility to him in a hygienic point of view.
Those which live in the water have other guardians: instead of
insects, we find a number of crustaceans which establish themselves on
fishes, and if there are no scales of the epidermis which annoy them,
there are mucosities which are incessantly renewed in order to protect
the skin from the continual action of the water.
We find many on the surface of the scales, and others which conceal 69
themselves at the bottom of mucous canals. We have brought together
only a few examples, and there are certain others which are mentioned
elsewhere, but which ought more properly to be placed here.
The insects long known under the name of _Ricini_, and to which
many other appellations have been given, deserve to figure in the
first rank in this group. They have always perplexed entomologists,
who seem to consider them as parasites allied to acaridæ and lice. It
has, however, been long known that they have no trunk to suck with,
and that they have two small scaly teeth, which rather serve for the
purpose of biting. A long time since, the examination of their stomach
proved that they contain only morsels of skin instead of blood. This
has induced many entomologists to place them in the same order as
grasshoppers, that of Orthoptera.
Lyonet has given figures of several of those which he studied with the
care which he so well knew how to employ in his anatomical
investigations; and in 1818 Nitzsch, a professor at Göttingen, had
brought together so great a number of them, that it required several
days to examine his collection; he began the publication of his
catalogue, but has not had time to finish it. Several other
entomologists and anatomists have since taken up the subject.
We owe the description of several hundred species to Mr. Denny. Mons.
F. Rudow has lately made known a great number of species which he has
collected from the skins of birds coming from Japan, Australia, 70
Africa, and the two Americas.
Professor Grube, of Breslau, has published the description of the
insects and acaridæ found during the travels of Middendorf in Siberia.
These descriptions relate especially to the Philopteræ of birds, the
Pediculinæ of the mammalia, a flea of the _Mustela Siberica_, and an
acarus of the _Lemmus_. Quite recently, an American naturalist, Mr.
Packard, who has undertaken the study of so many different subjects,
has published in the "American Naturalist" the description,
accompanied by an engraving, of the _Menopon picicola_, found on the
_Picoides Arcticus_ from the lower Geyser basin, Wyoming territory,
also of the _Goniodes Merriamanus_, the _Tetrao Richardsoni_, and the
_Goniodes mephitidis_, found on a _Mephitis_ from Fire-Hole Basin,
Wyoming territory; of the _Nirmus buteonivorus_, from a _Buteo
Swainsonii_; and of _Docophorus Syrnii_, from _Syrnium nebulosum_.
A great number of these insects live between the feathers of birds,
and can be more easily observed, since they detach themselves after
the death of their host. They are easily found on the skins of birds
prepared for museums. These ticks form a family under the name of
_Riciniæ_, and this family is divided into two parts, the _Liotheidæ_
and the _Philopteridæ_.
Among the many generic divisions, one of the most interesting has
received the name of _Trichodectes_; it contains twenty species, one
of which lives on the dog, another on the cat, another on the ox; in a
word, we discover a distinct species on each of the domestic mammals.
It has been said that the _phthiriasis_ of the cat is occasioned by 71
the abundance of ricini. The trichodectes of the dog has lately
attracted the especial notice of naturalists, and that from the
following circumstances.
There is no tape-worm more common in the dog than the _Tænia
cucumerina_. But whence comes it? How is it introduced? This had been
an enigma for many years, at the time when I dissected some dogs
infested with _Tænia serrata_, in the Museum of Natural History at
Paris. Together with the _Tænia serrata_, the number and age of which
I knew beforehand, since I had myself _planted_ them, there were found
in the intestines of one of the dogs some individuals of the _Tænia
cucumerina_. My dogs had taken nothing but milk, and _cysticerci
pisiformes_. Were there cysticerci of different kinds in the
peritoneum of the rabbit? The veil is now withdrawn. We have just said
that the dog harbours a tick known under the name of Trichodectes, and
in this trichodectes lodges the Scolex, we might even say the larva of
the _Tænia cucumerina_. Dogs, especially young ones, lick their hair
continually, and it is by this operation that the young tænia is
introduced. It is by a similar process that the horse introduces the
eggs of the OEstrus which are hatched in its stomach.
Many of these ticks live abundantly in birds, and multiply rapidly.
The _Liothe pallidum_ lives on the cock, the _Liothe stramineum_ on
the turkey, the _Philopterus falciformis_ on the peacock, the
_Philopterus claviformis_ on the pigeon. It is to be observed that
every bird can nourish many different kinds. Fig. 2 represents the
tick which infests the sea-eagle, called Pygarg.
[Illustration: Fig. 2.--Ricinus of the Pygarg.] 72
Fishes harbour crustaceans instead of ticks, and their number is not
less considerable than on mammals and birds. These crustaceans have
perplexed naturalists more than once, because they could only regard
them as parasites. They live on the produce of cutaneous secretions,
and if they improve, as do the ticks, the cleanliness of their host,
they are not less useful in a hygienic point of view, for they prevent
the accumulation of cutaneous productions.
Among these crustaceans, we must mention the _Caligi_ and the
_Arguli_, which never become bloated, the _Ancei_, and probably other
genera. Instead of the ungainly and unusual forms of true parasites,
they all preserve, together with their fishing tackle and locomotive
apparatus, their neat and elegant appearance. The sexes even differ
only in size. They remain during the whole of their life what they are
at the beginning; that is to say, charming in form, with a
delicately-shaped corselet, numerous and slender claws, and are as
graceful in their movements as when in a state of rest. The greater
number of osseous fishes lodge Caligi on the surface of their skin.
These fix themselves by means of strong cables, but without
sacrificing their liberty. They are usually called fish lice.
Fishermen, when returning from the northern fishery, generally find
their vivarium full of these graceful vermin. It may be said that 73
the caligi are common everywhere, and that each species has its own
caligi. The fishes of the family Plagiostoma, notwithstanding the
hardness of their skin, afford food to some of these; they multiply so
rapidly sometimes, that they cover their host as though they took the
place of scales. The cod gives lodging to a charming species of a very
beautiful shape, which in its turn, affords a resting-place to the
Udonella. It is always attached to the ovisacs, and doubtless plays
the same part as the Histriobdellæ, so that we shall find the Caligi
attending to the toilet of the cod, and the Udonellæ in their turn
waiting on the Caligi.
[Illustration: Of the natural size.]
[Illustration: _Caligulus elegans_ (fem.)]
The name Arguli has been given to some crustaceans which resemble the
caligi in size and in manner of life, and which principally frequent
fresh-water fishes. The _Argulus foliaceus_ is the name of the
species which has been known for the longest time, and which is most
extensively found. It is to be seen on our pikes, carps, sticklebacks, 74
and on the greater part of our river fish. Mr. Thorell, in his
monograph, mentions twelve species of Arguli proper, and four species
of which he composed the genus _Gyropeltis_. Four are found in Europe,
two of which are on salt-water, and two on fresh-water fish.
Quite recently, Professor Leydig has made known another species living
on the _Phoxinus levis_. Arguli are met with on the fishes of Africa,
the Indies, and North and South America. Like the caligi, these
animals spontaneously abandon one host, to go and attend to the toilet
of another.
Another animal, which has been taken for a Lernæan, deserves to take
its place by the side of the Caligi, at least on account of its manner
of life. We refer to that singular being which Leydig discovered in
1850 in Italy, while studying the mucous canal of a _Corvina_, at
Cagliari, and to which he gave the name of _Sphoerosoma_. To judge by
the plate and by some details, this _Sphoerosoma_, the name of which
ought to be changed to _Leydigia_, belongs, if we mistake not, to the
same group as the Histriobdellæ. We are persuaded that the first
opportunity will confirm the correctness of this alliance, by the
study of its embryonic form. If we had not been able to examine into
all the development of the Histriobdellæ, more than one naturalist
would have considered them Lernæans, as happened at the congress of
German naturalists at Carlsruhe.
If we see many of these crustaceans live a joyous life while young,
there are others which seem to practise economy, and to emancipate
themselves when they have grown old. Mons. Hesse and Mr. Spence Bate a
few years since revealed the secrets of their existence.
Naturalists had recognized some crustaceans under the name of 75
_Ancei_, and others under the name of _Pranizæ_, living together upon
fishes, but with very different organs for fishing and swimming.
M. Hesse, curious to know the manner of life of the Pranizæ, made
observations on them in a small aquarium, and he perceived that the
parts of the mouth were all at once transformed into formidable
mandibles, which caused them to resemble Ancei. As it had often
occurred with respect to other groups, that the same crustacean at
different periods of its evolution had been taken for different
animals, the naturalist of Brest had some suspicion as to their
identity, and soon ascertained by direct observation that he had not
been mistaken. The Pranizæ become Ancei, and live upon fishes under
their first form, like caligi and arguli. Nothing can be seen which is
more curious than these crustaceans, which ride on the back or the
sides of fishes, and assume there every possible attitude.
The Pranizæ fix themselves in the mouth and in the gills as well as on
the skin. Some are found on sharks as well as on osseous fishes. They
fear neither heat nor light, and do very well under damp sea-weed
while waiting for the return of the tide. They run and swim with the
same facility. When in the condition of Ancei, they lose their
agility, and, under this form, all denotes their sedentary habits.
They appear to live in holes, at the bottom of which they defend
themselves with their powerful mandibles. It has been observed that
fecundation is accomplished, as in the _Axolotls_, before the
evolution is complete, but that the eggs are not laid until the animal
assumes the form of Anceus.
We may here remark that the change of appearance takes place only 76
among the females; the males preserve their dress and their liberty.
Some naturalists assert that we must not accept the metamorphosis of
either sex as an established fact, except for the purpose of
arrangement. All, however, tends to show that Mons. Hesse has fairly
interpreted facts; but it appears to us probable that the whole of the
history of these strange crustaceans is not fully known.
Fishermen have long since known whale-lice, the _Cyami_ of
naturalists, of which we have already made mention while speaking of
free messmates. They live at liberty on the skin of their host, and
multiply with extreme rapidity. These Cyami have a regular form, but
completely different from the others, and have given (like the Ricini
and the afore-mentioned crustaceans), great trouble to systematic
zoologists. The place which they ought to occupy is far from being
definitely fixed. At all events they may be considered as a shorter
kind of Caprellæ.
As each whale has cirrhipedes which are peculiar to itself, so each
has its own cyami. Professor Lütken, of Copenhagen, has made known ten
or twelve species, all found on cetacea, in the two hemispheres. The
supposed Cyamus, represented by Dr. Monedero as living on the Biscayan
whale, is a Pycnogonon.
The Anilocræ and the Nerocilæ, like the Cyami and other genera,
establish themselves on the back of a fish which is a good swimmer.
Jealous of their liberty, they preserve their oars and their fins, in
order to change their convoy, when the desire seizes on them, and do
not imitate the Bopyrians, which instal themselves on the narrow 77
branchial cavity of some decapod crustacean, and as soon as they have
entered, throw off all their travelling baggage; in fact, there is no
other means for them to gain admission; their lot is identified with
that of their host; they can no longer live without him. The female
only, it is true, thus renounces her liberty; she sacrifices herself,
as usual, for her family, while the male, far from giving himself up,
preserves his defensive arms, his claws, and his liberty.
The crustaceans called Caprellæ are perhaps not so independent as they
appear to be; it is not impossible that their place may be among the
crustaceans now under our consideration. They are often found,
together with the Tanaïs, on the bodies of cetaceans and chelonians,
on plagiostomous fishes, or in the midst of colonies of Sertulariæ.
They also establish themselves on buoys when they are well covered
with animal life; and we have discovered them in prodigious numbers on
a piece of cable which had lain at the bottom of the sea, and the
whole surface of which was covered with animals of every kind.
We may here mention the Pycnogonons, the Saphyrinæ, the Peltidiæ, and
the Hersiliæ; these crustaceans often crawl over the skins of their
congeners, but without ever renouncing their independence; and they
are all more or less occupied with the toilet of their neighbours.
We shall place in a second section some animals which have been
usually classed among parasites, rather because of their living upon
their neighbours than on account of their mode of life. If it is
necessary in menageries to have keepers to cleanse the animals
themselves, it is as requisite to have others to keep the cages 78
clean, and to remove dung and filth. Many animals perform this office.
The rectum of frogs is always literally full of _Opalinæ_ which
swarm in this cavity, like ants in their ant-hill, and doubtless live
on the contents of the intestine.
These Opalinæ are true infusoria, which do not wait till the fecal
matters are decomposed, and till the waters are corrupted by their
presence; they prevent accidents which might arise, and interfere in
time to purify the water from these excretions. There have been found
hitherto in the rectum of frogs, and in the different annelids, the
Pachydrili, the Clitelides, the Lumbriculi, and the Enchytrei. We have
also seen them in the Planaria and the Nemertians. There is no sight
more curious for those who are commencing microscopical studies, than
the examination of the contents of the rectum of these Batrachians.
Van Leeuwenhoeck knew, two hundred years ago, those animalculæ, to
which Bloch at a later period gave the name of _Chaos intestinalis_.
There are also some Rotatoria, the _Albertiæ_ for example, which ought
to have a place here, and which Dujardin has described and named. They
live in the intestines of the Lumbrici and of snails, and in the larvæ
of Ephemerides.
Dujardin first pointed out the _Albertia vermiculus_; since then Mons.
Schultze has made known the Albertia of the _Näis littoralis_, and
Radkewitz has recognized in the small worm of our gardens the
_Enchytreus vermicularis_. Long since, Siebold correctly stated that
these animals are not parasites, since they do not live at the expense
of their host.
There is a worm in the Philippine Islands, as Professor Semper has 79
informed me, which lodges in the intestines of a fish, with its head
usually projecting outwards, and which watches the crustaceans
attracted by the excreta of its host; but although it chooses the
intestine of its neighbour as a place of shelter, it is not a
parasite.
Fishermen affirm, and the examination of the animal's stomach confirms
their assertion, that the _Cyclopterus lumpus_ feeds on nothing
but the excreta of other fishes. Indeed, it is not possible to count
the number of intestinal worms known by the name of _Scolex_, which
are found in the contents of the stomach and the intestines. Besides
this, we have long known the peculiarities of some insects which
cannot live except on the dung of certain animals; and there is an
example of one of these insects, found in a fossil state, which
anticipated the discovery of the remains of an extinct mammal before
unknown in that district. The larvæ of the fly _Scatophaga
stercoraria_ live only on excrementary matter.
There are also nematode worms which exist under these conditions, and
which develop and propagate their species in the intestines as if in
the midst of damp earth. The small eel-like creatures so abundant in
cow-dung propagate in it; they are not parasites, and are allied to
those of which we speak in this chapter.
Besides those attendants which busy themselves about the cleanliness
of other animals, we find some whose duties are less extensive, and
whose cares are more limited. Many animals produce a greater number of
eggs than they can bring to perfection, and those which are decomposed
for want of fecundation, or which die in the course of evolution, 80
are under the care of an especial attendant, employed to make away
from time to time with the addled eggs, or the embryos that have
failed to come to maturity.
In this manner lobsters give lodgings in the midst of their eggs to a
worm, which we at first took for a Serpula, and which, after a
complete examination, turns out to be one of the Hirudinidæ: we have
given it the name of _Histriobdella_. It is as singular in its
movements as in its conformation, and its manner of living approaches
that of the _Pontobdellæ_ of the rays, of which we shall speak
subsequently. We announced this discovery a few years ago in the
following terms:--
It is known that lobsters, as well as crabs and the greater part of
the crustacea, carry their eggs under the abdomen, and that these eggs
remain suspended there till the embryos are hatched. In the midst of
them lives an animal of extreme agility, which is perhaps the most
extraordinary being which has been subjected to the eyes of a
zoologist. It may be said, without exaggeration, that it is a biped,
or even quadruped, worm. Let us imagine a clown from the circus, with
his limbs as far dislocated as possible, we might even say entirely
deprived of bones, displaying tricks of strength and activity on a
heap of monster cannon balls, which he struggles to surmount; placing
one foot formed like an air-bladder on one ball, the other foot on
another, alternately balancing and extending his body, folding his
limbs on each other, or bending his body upwards like a caterpillar of
the geometridæ, and we shall then have but an imperfect idea of all
the attitudes which it assumes, and which it varies incessantly.
Its rank and its affinities would have given rise to long discussions 81
if we had not made known at the same time its evolution and anatomical
structure.
It is neither a parasite nor a messmate; it does not live at the
expense of the lobster, but on one of the productions of these
crustaceans, much in the same manner as do the Caligi and the Arguli.
The lobster gives him a berth, and the passenger feeds himself at the
expense of the cargo; that is to say, he eats the eggs and the embryos
which die, and the decomposition of which might be fatal to his host
and his progeny. These Histriobdellæ have the same duty to perform as
vultures and jackals, which clear the plains of carcases. That which
causes us to suppose that such is their appropriate office, is that
they have an apparatus for the purpose of sucking eggs, and that we
have not found in their digestive canal any remains which resemble any
true organism. We find the feces, rolled up as balls, placed after
each other in their intestines.
The crustaceans also feed other Hirudinidæ. Mons. Leydig has noticed a
_Myzobdella_ on the _Lupa diacantha_. The fresh-water crab, common in
all the rivers of Europe, nourishes two, the _Astacobdella roeselii_,
which lives under the abdomen, or about the eyes, and the
_Astacobdella Abildgardi_ which especially frequents the branchiæ. Two
astacobdellæ on the same crab doubtless play different parts. We
should almost venture to assert, _à priori_, that the species in the
gills lives as a parasite on the blood of its host, whilst the other,
lodged under the abdomen, plays the same part as the histriobdella of
the lobster.
We often find among the eggs of the ordinary crab of our coasts 82
(_Cancer moenas_) a nemertian which probably performs the same
office. He is lodged while young in a kind of firm sheath attached to
the abdominal processes. We have been able easily to study the first
phases of its evolution. We have given it the name of _Polia
involuta_.
This nemertian had been observed at Messina, and described before by
Kölliker under the name of _Nemertes carcinophilus_, and it has
just been described and figured anew by Mr. M'Intosh, in a monograph
of British annelids published by the Ray Society.
The sturgeon seems to give lodging in its eggs to a polyp which plays
the same part. In fact, Mons. Owsjannikoff, at the congress of Russian
naturalists at Kiew, described an animal, _Accipenser ruthenus_,
which lives in the eggs of the sterlet. Some eggs placed in water for
a few hours at first show tentacles on the outside, then a whole
colony, and each part consists of four individuals, which have a
common digestive cavity, resembling somewhat a hydra divided
longitudinally in four. Each has six tentacles, two of which are
terminated by transparent corpuscles, perhaps nematocysts; the
digestive cavity extends into the arms, as in the hydra; the mouth is
not between the tentacles, but at the opposite pole. They are not all
lodged within the eggs; some are found outside, according to the
observations of Mons. Koch. Does not this animal fulfil in the egg of
the sterlet, the same office as the histriobdella in the egg of the
lobster?
The eggs of some insects are attacked by very little ichneumons, the
_Proctotrupidæ_; they empty them, and then instal themselves in
the shell. Mons. Fabre has mentioned, in his memoir on the habits of 83
the _Meloë_, a worm found in an egg.
M. Barthelemy has studied a nematode worm (_Ascaroides limacis_)
which inhabits as a parasite the egg of the grey snail; is this not
the ordinary worm of the snail which has introduced itself into the
eggs?
Many animals establish themselves on their neighbours, not to obtain
any advantage from them, except to profit by their fins; they are not
themselves sufficiently adapted to rapid motion, so they seize a good
courser, mount on his back, and ask from him only a resting-place and
no provisions. But it is often very difficult to say where
commensalism ends and mutualism begins; the cirrhipedes, for example,
establish themselves on a piece of floating wood, or on the bottom of
a vessel; on a block of stone, or on one of the piles of a groin; on
an immovable animal as well as on a good swimmer.
Some fourteen years ago, Jacobson of Copenhagen wrote an interesting
essay, to show that the young bivalves that are found in the branchiæ
of anodonts at a certain period of the year are parasitical animals,
for which he proposed a new name. But these supposed parasites are
only young anodonts, which by the help of a very long cable, which
proceeds from their foot like a byssus, attach themselves to their
mother, or to a fish which will carry them to a distance.
We see full-grown acephalous molluscs, as mussels and pinnæ, still
keep these cables, under the name of byssus, during their whole life.
There are also among distomians, worms which though they are
hermaphrodite, couple two and two, and have this additional
peculiarity, that while one increases rapidly the other becomes 84
atrophied.
An Egyptian distome, which lives in man, gives an instance of this
peculiarity, as well as the _D. filicolle_, which inhabits a fish
(_Brama Raii_). The caligi which live on the skin of fishes are,
when young, fastened by a cord which comes from the anterior edge of
their carapace: while quite little, they put themselves under the
protection of a kind neighbour, and allow themselves to be led by him.
The new tubularia, which we have dedicated to our learned colleague
Dumortier, often fixes itself on the carapace of ordinary crabs, and
causes itself to be conveyed like the Echeneis; the tubulary observed
by Gwyn Jeffreys, close by the eye of the _Rossia papillifera_, a
cephalopod mollusc, perhaps belongs to the same species.
Every colony of campanulariæ or sertulariæ lodges a crowd of messmates
and mutualists; and there are a great number of crustaceans and polyps
of all sizes which serve as an abode for infusoria of every kind. Some
establish themselves on the carapace or on the swimming appendages, as
in a carriage; others on one of the gills, which renders their mode of
life more easy, and the danger less great. An amphipod very
extensively spread over our sea-coasts, the _Gammarus marinus_,
usually has its appendages covered with _Vayinicola crystallina_.