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So curious a provision for the safety of the young in the pipe-fish may be compared to some extent, as I hinted above, with the pouch in which kangaroos and other marsupial animals carry their cubs after birth, till they have attained an age of complete independence. But the strangest part of it all is the fact that while in the kangaroo it is the mother who owns the pouch and takes care of the young, in the pipe-fish it is the father, on the contrary, who thus specially provides for the safety of his defenceless offspring. And what is odder still, this topsy-turvy arrangement (as it seems to us) is the common rule throughout the class of fishes. For the most part it must be candidly admitted by their warmest admirer, fish make very bad parents indeed. They lay their eggs anywhere on a suitable spot, and as soon as they have once deposited them, like the ostrich in Job, they go on their way rejoicing, and never bestow another passing thought upon their deserted progeny. But if ever a fish does take any pains in the education and social upbringing of its young, you’re pretty sure to find on enquiry it’s the father–not as one would naturally expect, the mother–who devotes his time and attention to the congenial task of hatching or feeding them. It is he who builds the nest, and sits upon the eggs, and nurses the young, and imparts moral instruction (with a snap of his jaw or a swish of his tail) to the bold, the truant, the cheeky, or the imprudent; while his unnatural spouse, well satisfied with her own part in having merely brought the helpless eggs into this world of sorrow, goes off on her own account in the giddy whirl of society, forgetful of the sacred claims of her wriggling offspring upon a mother’s heart.

In the pipe-fish family, too, the ardent evolutionist can trace a whole series of instructive and illustrative gradations in the development of this instinct and the corresponding pouch-like structure among the male fish. With the least highly-evolved types, like the long-nosed pipe-fish of the English Channel, and many allied forms from European seas, there is no pouch at all, but the father of the family carries the eggs about with him, glued firmly on to the service of his abdomen by a natural mucus. In a somewhat more advanced tropical kind, the ridges of the abdomen are slightly dilated, so as to form an open groove, which loosely holds the eggs, though its edges do not meet in the middle as in the great pipe-fish. Then come yet other more progressive forms, like the great pipe-fish himself, where the folds meet so as to produce a complete sac, which opens at maturity, to let out its little inmates. And finally, in the common Mediterranean sea-horses, which you can pick up by dozens on the Lido at Venice, and a specimen of which exists in the dried form in every domestic museum, the pouch is permanently closed by coalescence of the edges, leaving a narrow opening in front, through which the small hippocampi creep out one by one as soon as they consider themselves capable of buffeting the waves of the Adriatic.

Fish that take much care of their offspring naturally don’t need to produce eggs in the same reckless abundance as those dissipated kinds that leave their spawn exposed on the bare sandy bottom, at the mercy of every comer who chooses to take a bite at it. They can afford to lay a smaller number, and to make each individual egg much larger and richer in proportion than their rivals. This plan, of course, enables the young to begin life far better provided with muscles and fins than the tiny little fry which come out of the eggs of the improvident species. For example, the cod-fish lays nine million odd eggs; but anybody who has ever eaten fried cod’s-roe must needs have noticed that each individual ovum was so very small as to be almost indistinguishable to the naked eye. Thousands of these infinitesimal specks are devoured before they hatch out by predaceous fish; thousands more of the young fry are swallowed alive during their helpless infancy by the enemies of their species. Imagine the very fractional amount of parental affection which each of the nine million must needs put up with! On the other hand, there is a paternally-minded group of cat-fish known as the genus Arius, of Ceylon, Australia, and other tropical parts, the males of which carry about the ova loose in their mouths, or rather in an enlargement of the pharynx, somewhat resembling the pelican’s pouch; and the spouses of these very devoted sires lay accordingly only very few ova, all told, but each almost as big as a hedge-sparrow’s egg–a wonderful contrast to the tiny mites of the cod-fish. To put it briefly, the greater the amount of protection afforded the eggs, the smaller the number and the larger the size. And conversely, the larger the size of the egg to start with, the better fitted to begin the battle of life is the young fish when first turned out on a cold world upon his own resources.