CHAPTER III. 53

FIXED MESSMATES.

The animals of which we have just spoken usually preserve their full and entire independence; from the time of their leaving the egg, till their complete development, they are subject to no other outward changes than such as belong to their class. If they sometimes renounce their liberty, it is only for a limited time; and they all preserve not only their peculiar appearance, but their organs intended for fishing or for locomotion. It is not thus with those which we are now about to consider; they are free in their youth, but as they draw near to puberty they make choice of a host, instal themselves within him, and completely lose their former appearance: not only do they throw aside their oars and their pincers, but they cease sometimes to keep up any communication with the outer world, and even give up the most precious organs of animal life, not even excepting those of the senses; they are installed for life, and their fate is bound up with the host which gives them shelter. The number of these messmates is considerable.

We shall first allude to some crustaceans named Cirrhipedes by Lamarck. The metamorphoses which they have undergone since they left the egg have so much changed them, that Cuvier and all the 54 zoologists of his age placed them in the class of mollusca. The incrustations of their skin resembled shells, which these creatures generally carry in the substance of their mantle.

These ambiguous creatures are far from being microscopic; there are Balani which attain the size of a walnut, and some have been found not less than ten inches high, as the _Balanus psittacus_. Some years since we saw on a piece of floating wood, found by fishermen in the North Sea, Anatifæ on the end of stalks from six to seven feet in length. The anatifæ themselves were of the usual size. These cirrhipedes belonged to every geological period; they have already been found in the Silurian formation, but, unlike the trilobites their contemporaries, they pass through all the ages, and, far from decreasing, they reign as masters at the present time in the two hemispheres.

It was an English naturalist, Thomson, who first made known the true nature of these singular organisms. So far were many from understanding their affinities with the other classes, that even after the excellent researches of the Belfast naturalist, they doubted their correctness, and supposed that these animals were allied both to the mollusca and to the articulata.

We see by this the immense progress which embryological studies have caused us to make in the appreciation of natural affinities. No one at the present time, who has seen a cirrhipede hatched, can retain any doubt as to the place which it ought to occupy. These crustaceans, taken as a whole, lead a life in which we find more than one 55 contrast; all live as wanderers when they first leave the egg, and they are hatched in such abundance on the coast, that the water becomes literally troubled with them. At the first period of their life, they have a supple and elegant body, and fins admirably divided, and the gracefulness of the postures which they assume does not yield in beauty to those of the most brilliant insect. After having spent some time in seeking adventures, they are seized with disgust for a nomad life; they choose a resting-place, and establish themselves by means of a cable which they afterwards abandon, and shelter themselves in an enclosed retreat for the rest of their days. Many cirrhipedes choose the back of a whale or the fin of a shark, and make the passage across the Atlantic or the Pacific in less time than the swiftest steamboats.

In many of these, recurrent development (I was about to say degradation) sometimes proceeds so far, that their animal nature becomes doubtful, and more than one of them, having no longer any mouth by which to feed, are reduced to a mere case which shelters their progeny. The messmate very nearly takes its rank among parasites. There are also cirrhipedes which live on different genera of their own family; and some species which are always found in society with other species. Some also live as messmates with each other; some of the Sabelliphili have one of the sexes parasitical on the other sex.

Crustaceans are usually dioecious; but because of their manner of life, the cirrhipedes sometimes unite the two sexes and thus render the preservation of the species more certain. The whole family of the _Abdominalia_, a name proposed by Darwin, if I am not mistaken, have the sexes separate; and the males, comparatively very small, 56 are attached to the body of each female. It is a case of polyandria which we see realized in the _Scalpellum_. Darwin made known the existence of supplementary males, so small and so little developed, that they are with difficulty discovered, and so badly are they provided with organs that they have neither those of motion nor a stomach to digest. We have not exhausted the strange peculiarities of this particular group; there are some which live without shells and claws in the inside of other cirrhipedes, and atrophied males which only exist at the expense of their own females.

It is almost useless to make the remark that more especially here there exist almost insensible gradations of difference between parasites, messmates, and free animals, and we shall find more than one example of this in the crustaceans to which we now allude.

The most interesting fixed messmates are evidently those cirrhipedes, which, under the name of _Tubicinella_, _Diadema_, or _Coronula_, cover the skins of whales. They are, like all the rest, free in their infancy, but soon they take shelter on the back or on the head of one of these huge cetaceans, which they never quit when they have once chosen their abode. That which gives them great importance is, that each whale lodges a particular species; so that the crustacean messmate is a true flag which indicates in some respect the nationality, and it would not be without interest for voyagers who are naturalists to study these living flags.

The great whale of the north, the _Mysticetus_, which our northern neighbours discovered while seeking for an eastern passage to India, a species which never leaves the ice, carries no cirrhipedes. 57 This fact was already known to Iceland fishermen of the twelfth century. The intrepid whalers of these regions used to distinguish a northern whale, without "calcareous plates," from a southern whale with plates, that is to say, with cirrhipedes. This latter whale is the celebrated species of temperate regions, the _Nord-Kaper_ which the Basques used to hunt, from the sixth century, in the Channel, and which they used afterwards to pursue even to Newfoundland. The whales of the southern hemisphere, like those of the Pacific Ocean, all have their own species of cirrhipedes. We found in the museum of the Zoological Garden at Amsterdam, a _Coronula_, brought from Japan by Mr. Blomhof, known under the name of _Coronulæ reginæ_, which, no doubt, characterizes the whale of those latitudes. Another northern whale, the _Keporkak_ of the Greenlanders, very remarkable for its long fins, which give it the name of _Megaptera_, is covered very early in its life with these crustaceans, so much so, that the Greenlanders imagine that they are born with them. Some even have pretended to have seen Megapteræ covered with these coronulæ before their birth. Eschricht has in vain offered a reward to him who would send him coronulæ still attached to the umbilical cord; he has only received some pieces of skin covered with hairy bulbs. There is no doubt that young whales have been seen and captured while following their mother, which were already covered by these crustaceans.

Steenstrup has indicated the presence of _Platycyamus Thompsoni_ on the body of the _Hyperoodons_, and the _Xenobalanus globicipitis_ on the globiceps of the Shetland Isles.

The _Cryptolepas_ is a new genus of Coronulidæ which inhabits the 58 coast of California, on the singular mysticete recently distinguished by the name of _Rhachianectes glaucus_. The _Platylepas bisexlobata_ has lately been observed on one of the Sirenia, the _Manatus latirostris_. The marine turtles are also invaded by these singular animals, and their peculiar form, joined to their habitat, has given them the name of _Chelonobia_. It is not uncommon to find by the side of these Chelonobiæ, and even upon them, the Tanaïs, Serpulæ, and Bryozoariæ, forming together an animal forest on the cuirass of the turtle. The _Matamata_, a turtle living in the brackish water of Guiana, is covered with a cirrhipede more allied to the ordinary balani than to the chelonobiæ. Other living reptiles are not more exempt from cirrhipedes than turtles; the _Dichelaspis pellucida_ and the _Conchoderma Hunteri_ invade different sea-snakes. Many sharks harbour particular kinds, among which we mention the _Alepas_ of the _Spinax niger_ from the coasts of Norway. The same Alepas has been found on the _Squalus glacialis_ at the same time as the _Anelasma squalicola_. Half a dozen varieties of these are known, one of which inhabits an echinoderm, another a decapod crustacean. These kinds of alepas are so reduced when they are adult, and are so completely despoiled of their distinctive attributes, that it is necessary to study them with especial care in their first dress, in order to recognize their parentage.

Other cirrhipedes establish themselves on neighbours of their own class, and we also find crustaceans upon other crustaceans. A pretty genus lives near Cape Verd on the carapace of a large lobster, and spreads itself on the centre of the back like a bouquet of flowers. My son has procured some very fine specimens, an account of which he 59 will publish, together with the other materials which he has collected during his passage across the Atlantic. Mr. John Denis Macdonald found in abundance on the branchiæ of a crab in Australia, the _Neptunus pelagicus_, which he places between the Lepas and the Dichelaspis.

The most singular, if not the most interesting of all these cirrhipedes, are the Gallæ, which appear under the tail of crabs or the abdomen of paguri, and which zoologists designate under the names of _Peltogaster_ or _Sacculina_. They are found in both hemispheres. The recurrent development is so complete, that we can no longer distinguish any organic apparatus unless it be that of reproduction, and the whole body is a mere case enclosing within its walls eggs and spermatozoids. We see them very frequently under the abdomen of the crabs of our coasts, or even on the segments of the bodies of paguri. Mons. A. Giard has lately studied these animals. It is during the coupling season, according to him, that the Peltogasters establish themselves upon the crabs. Professor Semper has brought back quite a collection of them from his voyage to the Philippine Islands, and has entrusted them to one of his pupils, Dr. Kussmann, for the purposes of study. We heard him with great interest, at the late Congress at Wiesbaden, explain with remarkable clearness the results of his learned and conscientious observations. We do not think that we shall be wrong in adding that, for a long time, we shall see nothing better or more complete on this subject. All those cirrhipedes which adhere by their head to the skin of their host, by means of filaments, are now designated by the name of _Rhizocephala_.

A curious opinion, quite recently expressed by a naturalist, Mons. 60 Giard, and which is a sign of the times, is that the Peltogaster of the Pagurus has become a Sacculina on the crab; the host having been transformed, its acolyte has done the same thing under the same influence.

Professor Semper has also found among the Philippine Islands, isopod crustaceans living as messmates after the manner of the peltogasters. Two cirrhipedes of the family of Peltogaster, the _Sylon Hippolytes_ and the _Sylon Pandali_, have been found by Mons. Sars under the abdomen of the _Pandalus brevirostris_.

There are cirrhipedes on the gasteropod molluscs. The _Concholepas Peruviana_, that beautiful shell which has long been considered a rarity in our collections, is frequented by the _Cryptophiolus minutus_, only a sixth of an inch in length. The _Scalpella_ often inhabit the Sertulariæ and other polyps; _Oxynasps_, _Creusiæ_, _Pyrgomæ_, and _Lithotryæ_ inhabit corals. Certain kinds of sponges are regularly invaded by the _Acastæ_ of Leach, eight species of which are mentioned by Darwin. As we find elsewhere parasites on parasites, here also we find messmates on messmates; on the common anatifa we perceive other genera, and on the _Diadema_ of the North Pacific, we almost always see _Otions_ and _Cineras_. The _Protolepas bivincta_ also, a fifth of an inch in length, lives as a messmate in the mouth of the _Alepas cornuta_; and the _Elminius_ of Leach also inhabits other cirrhipedes. The _Hemioniscus balani_, which Goodsir had taken some years ago for the male of the Balanus, is a messmate on these cirrhipedes. Parasites also are found in messmates; the soldier-crab gives lodging to the sexual _Eustoma truncata_ in its interior. 61 A macrourous crustacean which we ought to mention here, the _Galathea spinirostris_, Dana, frequents a comatula, the colour of which it assumes; it is the same without doubt with the _Pisa Styx_, which lives on a polyp known by the name of _Melitoea ochracea_.

If we pass from the crustaceans to the molluscs, we have to notice in the first place an elegant gasteropod, the _Phyllirhoa bucephala_, which carries on its head a singular appendage, the nature of which has only lately been known; J. Müller took it at first for a medusa, then he abandoned this opinion, when at length Mons. Krohn referred it definitively to the lower polyps; it differs from its congeners only by its form, its tentacular cirrhi, and its mode of life: it is the _Mnestra parasites_. There are a great number of acephalous molluscs, which we might mention as messmates, but we will only refer to the _Crenellæ_ which are regularly found in the substance of sponges.

The _Philomedusa Vogtii_ of Fr. Müller, which lives on the _Halcampa Fultoni_, undoubtedly deserves to be mentioned here as a fixed messmate. Many bryozoa spread themselves over marine animals, and often engage in a deadly struggle with their patron. But among all these bryozoa we must mention an animal very common on the sea-shore at Ostend, and which one would take for a dried leaf, the _Flustra membranacea_. On the surface of these imitative leaves are found little bouquets of other bryozoa, which are either _Crisiæ_ or _Scrupocellariæ_. Another kind, which has also passed for a gelatinous plant, bears the name of _Halodactylus_. Without any microscopic study, one can obtain an idea of these colonies. One of these 62 Halodactyles spreads itself upon the stalk of a Sertularia, all the inhabitants of which it stifles, so that it is the victim himself who serves as a guardian to the invader.

These Halodactyli are very widely spread over the Northern Seas, and often establish themselves on the large horse-hoof oyster. Michelin has noticed under the name of parasite a fossil _cellepore_ from the saltpits of Touraine and Anjou, which entirely surrounds the shell of a gasteropod; in order to prevent its patron from dying of hunger, the bryozoon develops itself around the mouth like a gallery, and prolongs its last spiral. This _Cellepora parasitica_ has evidently a place here.

Many of these messmate bryozoa are found in a fossil state in the crag of the Antwerp basin.

We have still to mention among fixed messmates many polyps, some of which are very remarkable. Thus, many naturalists speak of vast colonies of polyps in which lodge various animals which shelter themselves there like paguri in deserted shells.

Among these are the colonies of which Forster speaks, which are not less than three feet in diameter, and fifteen feet in height, with a crown of eighteen feet in diameter. Dana also makes mention of an _Astræa_ of twelve feet in height, and of _Porites_ twenty feet high, which contain more than five millions of individuals, among which a number of animals come to take refuge.

The Museum of Natural History at Paris is in possession of a superb specimen of _Porites conglomerata_: in the middle of the colony lodges a Tridacna (_Trid. corallicola_, Val.) like a pagurus under a forest of hydractiniæ. This remarkable polyp was brought from the Seychelles Islands by Mons. L. Rousseau. It is not impossible that pinnotheres 63 live in this same tridacna, and that we have there a fresh example of messmate within messmate.

In the Bay of Massachusetts, on the coast of New England, another curious messmate lives at great depths; Dana has lately described it, under the name of _Epizoanthus Americanus_, V. It establishes itself in the _Eupagurus pubescens_. The _Sertularia parasitica_ of the gulf of Naples, from which I have formed the genus _Corydendrium_, is a messmate after the manner of an infinite number of other polyps. In closing this list, we shall mention a polyp, named _Halicondria suberea_, and the _Actinia carcinopodus_ of Otto, which inhabit an univalve mollusc; as also the _Heterosammiæ_ and the _Heterocyathi_ of the family of Turbinolidæ, which lodge in a trochoid shell.

The sponges, placed by naturalists by turns among plants or on the confines of the animal kingdom, are now generally regarded as polyps; this is the opinion expressed by Haeckel, who wishes at the same time to replace the term Coelenterata by that of Zoophytes. The learned naturalist of Jena, when making this proposition, should have remembered that in 1859 we placed the sponges in the group of polyps, as the lowest in the scale; and that we proposed, from the time when the acalephæ were recognized to be adult polyps, to designate all these animals under the name of Polyps. Some time after, R. Leuckart proposed the appellation Coelenterate Polyps, which has been generally received. Professor Haeckel would have lost nothing by acknowledging that in 1873 he arrived at a result similar to that to which I had 64 come twenty years before, and that it is not a very happy innovation to change the term polyps for zoophytes. It is the more surprising that this naturalist has forgotten to quote my opinion, since at the congress of naturalists at Hanover in 1866, I had placed this question on the agenda for an ordinary meeting.

I maintained, in opposition to the opinion of the naturalists whose authority had been especially recognized in the matter (Osc. Schmidt, who was present, among others), that sponges are lower polyps, whether they are regarded as to their development or their organization.

This group, so remarkable in form, so varied in colour and appearance, very often affords examples of animals which live with them as true messmates; and we find the same relations established between them in both hemispheres. As we observe rhizophales on crabs and soldier-crabs, and pinnotheres on bivalve molluscs, so we find that the sponges of the Indian Seas or of Japan harbour the same messmates which we discover on them in the Northern Seas or the Atlantic.

In the sea of Japan is found a very remarkable sponge, generally known by the name of _Hyalonema_. It is a bundle of spicules like threads of glass, which seem artificially tied together, and on the surface of which we regularly find a polyp of the genus _Polythoa_. The nature of this sponge, and its relations with the polyps which surround it, have been discussed for many years. Ehrenberg had recognized the polyp Polythoa around the spicules, but the Hyalonema was considered by him as an artificial product. The _Polythoæ_ were regarded as only a case in which had been placed this bundle of spicules. The learned microscopist of Berlin had even thought that he had found the proof 65 of this opinion in the presence of woollen threads which were observed in a specimen which Mons. Barbosa du Bocage had sent him from Lisbon. Woollen threads had indeed adhered to the spicules of Hyalonema, but they came from the fishermen, who, when they drew these sponges from the water, placed them carefully in their bosoms under their woollen jerseys.

Dr. Gray, of the British Museum, considers the sponge as a parasite of the Polythoa, and that the bundle of spicules belongs, not to the sponge, but to the polyp. The most learned naturalist on the subject of sponges, Mr. Bowerbank, expresses a different opinion. The sponge and its spicules, according to him, are but a single body, and the polyps are only a part of it. The supposed polyps would only form a cloacal system for the use of the sponge colony.

Valenciennes, guided no doubt by the observations of Philippe Poteau, was the first to recognise the nature of the sponge and its spicules, but it is to Max Schultze that we must give the credit of distinguishing the true character of this extraordinary marine production. He has shown that the bundle is formed by the extraordinarily long spicules of the sponge, and that the polyp establishes itself upon it, by forming a sheath around the bundle.

The fact is no longer doubted by any one, that the long spicules form part of the sponge, and that the polyp establishes itself on a part of the colony. But science rarely advances by a single stride, and Max Schultze, like his predecessors, mistook the top of the sponge for 66 the bottom; Professor Loven has shown the true pose of the Hyalonema, and this he has effected by means of a small specimen from the Northern Sea.

Semper found a new OEga, to which he gave the specific name of _Hirsuta_, in an enlarged canal of the new Hyalonema of the Philippine Islands, which he dedicated to Mons. Schultze.

The Adriatic also produces a species of the same genus (_Polythoa_) which inhabits, like that of the Chinese Sea, a sponge to which the name of _Axinella_ has been given. These Polythoæ are only found on the Axinellæ, says Osc. Schmidt, who has especially studied the sponges of this sea and of the Mediterranean. Professor Gill mentioned at the last meeting of the scientific congress at Portland (1873), a new Hyalonema found on the coast of North America by the fishery commission of the United States. A memoir on these sponges, interesting in a systematic point of view, is due to the pens of Herklots and of Marshall.

We think that we ought to place among fixed messmates a very problematical organism which lives on Sertulariæ, especially on the _Sertularia abietina_, and which Strethill Wright has designated by the name of _Corethria sertularia_. Claparède has given to this singular animal the more expressive name of _Ophiodendrum abietinum_.

We have regularly found it on the _Sertularia abietina_ at Ostend, 67 every time that we have had an opportunity of observing these polyps immediately that they have been raised from the bottom of the sea. It is an organism whose affinities are not yet established.