Creator and a Divine

[Pg xxviii] Wisdom, who has created the heavens and the earth according to an eternal and preconceived plan, can alone resolve the enigmas of nature, as well as those of human life. Let us still erect statues to men who have been useful to their fellow-creatures, and have distinguished themselves by their genius, but let us not forget what we owe to Him who has placed marvels in each grain of sand, a world in every drop of water.”

At first we shall treat of animal messmates, secondly of mutualists, and thirdly of parasites.

ANIMAL PARASITES

AND MESSMATES.

CHAPTER I.

ANIMAL MESSMATES.

The messmate is he who is received at the table of his neighbour to partake with him of the produce of his day’s fishing; it would be necessary to coin a name to designate him who only requires from his neighbour a simple place on board his vessel, and does not ask to partake of his provisions.

The messmate does not live at the expense of his host; all that he desires is a home or his friend’s superfluities. The parasite instals himself either temporarily or definitively in the house of his neighbour; either with his consent or by force, he demands from him his living, and very often his lodging.

But the precise limit at which commensalism begins is not always easily to be ascertained. There are animals which live as messmates with others only at a certain period of their lives, and which provide for their own support at other times; others are only messmates under

certain given circumstances, and do not usually merit this appellation.

In the higher animals, this relation between them is generally well known, and justly appreciated, but it is not the same in the inferior ranks; and more than one animal may pass for a messmate or a parasite, for a robber or for a mendicant, according to the circumstances under which he is observed. The sharper passes for an honest man as long as he has not been taken in flagrante delicto. Thus, in order to be just, we must carefully examine the indictment, and not pronounce sentence without strict examination.

The greater part of those animals which have established themselves on each other, and live together on a good understanding and without injury, are wrongly classed as parasites by the generality of naturalists. Now that the mutual relations of many of these are better understood, we know many animals which unite together to render each other mutual assistance; while there are others which live like paupers on the crumbs which fall from the rich man’s table. There are many relations between the different species which can be discovered only after minute examination, but which have recently been appreciated with greater impartiality.

Animal messmates are rather numerous, and commensalism has been observed, not only in animals of the present age, but in those of the primary epoch. Wyville Thomson explained to me, while I was myself his messmate at Edinburgh, at the meeting of the British Association in 1871, that the polyps of the Silurian age already practised it. We do not class among animal messmates those living creatures which, like the birds 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