that to which I had 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 Polythos 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 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

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sponge for 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 Ega, 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 mess

Fig. 1.-Ophiodendrum abietinum on Sertularia abietina.

mates 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, 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.

CHAPTER IV.

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.