which we keep in cages, charm the ear with their song, or which, in spite of our care, live at the expense of our pantry; we will only refer to veritable messmates, which, sometimes through weakness of constitution, sometimes for want of activity, can neither feed themselves nor bring up their family without seeking help from their neighbours.

There are some free messmates which never renounce their independence, whatever may be the advantages which their Amphitryon enjoys; they break their alliance with him for the slightest motive of discontent, and go and seek their fortune elsewhere. Their susceptibility or their love of change guides them. They are recognized by their fishing implements or their travelling gear, which they never lay aside. These free messmates are the more numerous. The others, the fixed messmates, instal themselves with a neighbour, and live at their ease, having completely changed their dress, and renounced for ever an independent life. Their fate is thenceforward bound to him who carries them.

Under these two categories we shall cite several examples, and glance at the differences which the various classes of the animal kingdom present in this respect, beginning with the higher ranks.

CHAPTER II.

FREE MESSMATES.

WE meet with free messmates in various classes of the animal kingdom. They sometimes mount on the back of a neighbour, sometimes occupy the opening of the mouth, the digestive passages, or the exit for the excreta; at times they place themselves under the shelter of the cloak of their host, from whom they receive both aid and protection.

Among the vertebrates, there are few except fishes which merit a place here; it is only amongst these that we meet with species at the mercy of others, and dependent on acolytes, which are in every respect inferior to themselves.

An interesting messmate belonging to this first category is a fish of graceful form, named donzelina, which goes to seek its fortune in the body of a holothuria. Naturalists have long known it under the name of Fierasfer. It has a long body like that of an eel, entirely covered with small scales; and as it is quite compressed, it has been compared to the sword which conjurors thrust into their œsophagus. They are found in different seas, and all have similar habits. This fish is lodged in the digestive tube of his companion, and,

without any regard for the hospitality which he receives, he seizes on his portion of all that enters. The Fierasfer contrives to cause himself to be served by a neighbour better provided than himself with the means of fishing.

Dr. Greef, at present Professor at Marbourg, found at Madeira a holothuria of a foot in length, in which a vigorous Fierasfer lived in peace. Quoy and Gaimard, in the account of their voyage round the world, have remarked long since, that the Fierasfer hornei is found in the Stichopus tuberculosus.

The holothuriæ seem to exist under very advantageous conditions in this respect, since we see Fierasfers, which are themselves tolerable gluttons, accompanied by Palæmons and Pinnotheres in the same animal. Professor C. Semper has seen holothuriæ in the Philippine Islands which bore a considerable resemblance, in this respect, to an hotel with its table d'hôte.

These singular fishes have been long noticed, but it was not till recently that their presence in a host so low in the scale as a holothurian could be explained.

But if naturalists are agreed as to the bond which unites these fishes to the holothuriæ, they do not agree as to the organs which they inhabit in their living hotel. Do they lodge in the digestive cavity of the holothuriæ, or do they inhabit the arborescent respiratory processes which open at the posterior extremity of the body? Until recently it was thought that it was in their stomach, but a doubt has arisen. Professor Semper, who has studied these animals with particular care at the Philippine Islands, had the curiosity to open

the stomach of some of them, and found there, not the animals taken by the holothuriæ, but the remains of its respiratory processess which they were in the act of digesting. Is it then merely a messmate? We must have more information on this point; and if it were not accidentally that the fierasfer swallowed the walls of the compartment in which he was lodged, he ought rather to take his place among parasites. Though it lodges in the respiratory processes, as the learned professor at Wurtzburg asserts, the fierasfer may also be a messmate after the fashion of so many others which inhabit the neighbourhood of the rectum, in order the more conveniently to snap up those animals which are attracted by the odour.

The fierasfers are not the only fishes which seek assistance from the holothuriæ; a species lives at Zamboanga, to which the specific name of Scabra has been given, and in the stomach of which, says Mons. Johannes Müller, usually lives a myxinoid fish, called Enchelyophis vermicularis. Unfortunately, we are not told in what part of the stomach it resides; for all is stomach in these animals.

It is less degrading for a fish to ask assistance from one in his own rank. The Mediterranean offers a curious instance of this. Risso saw at Nice, at the commencement of this century, the monstrous fish known under the name of Beaudroie (the angler, or fishing-frog) lodging in its enormous branchial sac a fish of the family of the Murenidæ, the Apterychtus ocellatus. He is found there evidently under the condition of a messmate. Although the eels generally get their living easily, the Angler possesses fishing implements which are wanting in them, and

when both of them are immersed in the ooze, it carries on a fishery sufficiently abundant to enable it to share the spoil with others. This same angler lives in the northern seas, and there it harbours an amphipod crustacean, which until lately has escaped the vigilance of carcinologists. We shall speak of it further on.

Dr. Collingwood saw a sea anemone in the Chinese Sea, which was not less than two feet in diameter, and in the interior of which lodges a very frisky little fish, the name of which he could not tell.

Lieut. de Crispigny has observed a sea anemone (Actinia crassicornis) living on good terms with a malacopterygian fish, the Premnas biaculeatus. This fish penetrates into the interior of the anemone; the tentacles close round it, and it lives thus for a considerable time enclosed as in a living tomb. Mons. de Crispigny has kept these animals alive for more than a year, in order to make careful observations on them. A fish known by the name of Oxybeles lumbricoides has been also found in the Indian Seas, which modestly takes up his quarters in a star-fish (Asterias discoida). Another case of commensalism has been made known to us by Professor Reinhardt of Copenhagen. A siluroid of Brazil, of the genus Platystoma, a skilful fisherman, thanks to his numerous barbules, lodges in the cavity of his mouth some very small fishes, which were for a long time considered as young siluroids; it was supposed that the mother brought her progeny to maturity in the cavity of the mouth, as marsupials do in the abdominal pouch, or as some other fishes do. These messmates are perfectly developed and adult, but instead of living on the produce of their own labour, they prefer to instal them