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