mates, and each may perhaps have some of different sorts, and in diverse categories.

But whence come those disgusting beings, whose name alone inspires us with horror, and which instal themselves without ceremony, not in our dwellings, but in our organs, and which we find it more difficult to expel than rats or mice? They all derive their existence from their parents.

The time has passed when a vitiated condition of the humours, or the deterioration of the parenchyma was considered a sufficient cause for the formation of parasites, and when their presence was regarded as an extraordinary phenomenon resulting from the morbid dispositions of the organism. We have reason to hope that this language will, during the next generation, have entirely disappeared from works on physiology and pathology. Neither the temperament nor the humours have any influence on parasites, and they are not more abundant in delicate individuals than in those who enjoy the most robust health. On the contrary, all wild animals harbour their parasitical worms, and the greater part of them have not lived long in captivity, before nematode and cestode worms completely disappear. It is only the imprisoned parasites which do not desert them.

All these mutual adaptations are pre-arranged, and as far as we are concerned, we cannot divest ourselves of the idea that the earth has been prepared successively for plants, animals, and man. When God first elaborated matter, He had evidently that being in view who was intended at some future day to raise his thoughts to Him, and do Him homage.

This is the answer which I would give to the question recently propounded by Mons. L. Agassiz. "Were the physical changes to which our globe has been subjected effected for the sake of the animal world, considered in its relations from the very beginning, or are the modifications of animals the result of physical changes? in other words, has the earth been made and prepared for living beings, or have living beings been as highly developed as was possible, according to the physical vicissitudes of the planet which they inhabit?

This question has always been discussed, and that science which cannot look beyond its scalpel, will never succeed in resolving it. Each one must seek by his own reason the solution of the great problem.

When we see the newly-born colt eagerly seeking for its mother's teats, the chick as soon as it is hatched beginning to peck, or the duckling seeking its puddle of water, can we recognize anything but instinct as the cause of these actions, and is not this instinct the libretto written by Him who has forgotten nothing?

The statuary who tempers the clay from which to make his model, has already conceived in his mind the statue which he is about to produce. Thus it is with the Supreme Artist. His plan for all eternity is present to His thought. He will execute the work in one day, or in a thousand ages. Time is nothing to Him; the work is conceived, it is created, and each of its parts is only the realization of the creative thought, and its predetermined development in time and space.

The more we advance in the study of nature," says Oswald Heer in "Le Monde primitif" which he has just published, "the more profound also is our conviction, that

belief in an Almighty Creator and a Divine 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

B

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