at Geneva did not abandon this messmate before he had completely studied it. Let us remark in passing, that Professor Grube published in 1831, at Königsberg, a special work on the abodes of annelids in general.
Cases of commensalism among the Echinodermata are still more rare. These animals are sufficiently provided with organs, both with respect to their food and their skin, not to require the assistance of their neighbours. We cannot rank as a phenomenon of commensalism, the conduct of the young Comatulæ, which fasten themselves, as Mr. A. Agassiz informs me, to the basal cirrhi of the adult echinoderms, and there form a little colony of young Pentacrinites.
We only know one Ophiurus (Ophiocnemis obscura), which lives as a messmate on a comatula, and consequently seeks assistance from an animal of its own rank. Another kind of Ophiuride (Asteromorpha lævis, Lym.) fixes itself on a Gorgonella Guadelupensis of Barbadoes. Everything induces us to suppose that we shall find more than one species of echinoderm, which will take its place among these when their mode of life has been studied with greater care. Professor Lütken has just proved this by quite recently making known another Ophiothela, which lives in the straits of Formosa, and seems to be the messmate of an Isidian polyp, known under the name of Parisis loxa. Another species (Oph. mirabilis) from Panama, infests certain Gorgoniæ and sponges; a third is found in the Fiji Islands on the Melitodes virgata; a fourth at the Isle of France on Gorgoniæ; and a fifth at Japan on the Mopsella Japonica. There is also another in the Pacific Ocean, but its companion is not known.
Professor Mobius, as well as Dr. F. Martens, has noticed a Hemicuryale pustulata on a polyp of Jamaica, known under the name of Verrucella Guadelupensis. This is a curious instance of mimicry.
The class of polyps includes several species which seek for assistance from others, and are classed among messmates. One of the most remarkable is the Gigantic Medusa, which can extend its arms downwards to a hundred and twenty feet, and bears the name of Cyanea arctica; the disc is seven feet and a half in diameter, and when the animal is on the surface of the water, the fringes, which surround the cavity at its mouth, occasionally afford lodging in the midst of them to a species of actinia, which lives there as messmate. Sometimes three, and even four or five, are found on a single Cyanæa. This also is an observation due to Mr. A. Agassiz, which he has published in his interesting work, “Sea-side Studies.” Prof. Haeckel supposed that the Geryoniæ produce Œginidæ by means of buds; but it appears that the learned professor was mistaken as to the nature of these buds; that instead of being produced one from the other, they have, according to Steenstrup, a completely different genealogy, being only united by conditions of good-fellowship. They may be truly called messmates.
Mons. Lacaze-Duthiers, who went to the coast of Africa to study corals, met with a young polyp which requires the assistance of another polyp in its early condition. This animal, to which he has given the name of Gerardia Lamarckii, lives on one of the Gorgoniæ, which it invades and stifles, as the lianas strangle the tree over which they spread themselves. But these same Gerardiæ can also
develop themselves on the eggs of the Plagiostoma, and are then capable of living separately. In the substance of this polyp lives a crustacean, the nature of which Mons. Lacaze-Duthiers has not yet made known.
The superb sponge, Euplectella aspergillum, the elegant structure of which cannot be sufficiently admired, is, unlike the Alcyonium of the Dromia, rooted to the soil, but nevertheless gives shelter to three kinds of crustaceans: Pinnotheres, Palemonidæ, and Isopods. These supposed plants have been known for many years under the Spanish name of Regadera, or the English “Venus’ Flower-basket;” they were first brought from Japan, and afterwards from the Moluccas, and more recently from the Philippine Islands. In almost all the individuals which Professor Semper was able to study in those parts, were found the same crustaceans. These Euplectellæ have just been met with to the south-west of Cape St. Vincent, by Wyville Thomson, who has brought up some from a depth of 1090 fathoms, while on board the Challenger. This skilful professor has discovered another sponge to the north-west of Scotland, at a depth of 460 fathoms; it bears the name of Holtenia Carpenteri; and I have in my possession a fine specimen which I owe to his generosity, and keep as a souvenir of the delightful hospitality which he extended to me at the Edinburgh meeting.
There are also sponges which construct a dwelling in the abode of their neighbour. We find, among others, a small sponge known under the name of Clione, which establishes itself in the substance of the shell of oysters, and hollows out galleries as the teredo does in wood.
Mr. Albany Hancock found twelve species of Clione on a single Tridacna. They are evidently not parasites, and I am not sure if their place is properly among messmates. The oyster, and more especially the Ostrea hippopus, lodges three or four different sorts in its shell. These Cliones possess siliceous spicules, by means of which they hollow out galleries in the substance of shells. Mr. Hancock has published a monograph of this genus, in which he recognizes twenty-four species collected from different shells, and two other species, which he refers to the genus Thoasa.