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This is a general law, indeed, that runs through all nature, from London slums to the deep sea. Wasteful species produce many young, and take but little care of them when once produced. Economical species produce very few young, but start each individual well-equipped for its place in life and look after them closely till they can take care of themselves in the struggle for existence. And on the average, however many or however few the offspring to start with, just enough attain maturity in the long run to replace their parents in the next generation. Were it otherwise, the sea would soon become one solid mass of herring, cod, and mackerel.

These cat-fish, however, are not the only good fathers that carry their young (like woodcock) in their own mouths. A freshwater species of the Sea of Galilee, Chromis Andreae by name (dedicated by science to the memory of that fisherman apostle, St. Andrew, who must often have netted them), has the same habit of hatching out its young in its own gullet: and here again it is the male fish upon whom this apparently maternal duty devolves, just as it is the male cassowary that sits upon the eggs of his unnatural mate, and the male emu that tends the nest, while the hen bird looks on superciliously and contents herself with exercising a general friendly supervision of the nursery department. I may add parenthetically that in most fish families the eggs are fertilised after they have been laid, instead of before, which no doubt accounts for the seeming anomaly.

Still, good mothers too may be found among fish, though far from frequently. One of the Guiana catfishes, known as Aspredo, very much resembles her countrywoman the Surinam toad in her nursery arrangements. Of course you know the Surinam toad–whom not to know argues yourself unknown–that curious creature that carries her eggs in little pits on her back, where the young hatch out and pass through their tadpole stage in a slimy fluid, emerging at last from the cells of this living honeycomb only when they have attained the full amphibian honours of four-legged maturity. Well, Aspredo among cat-fish manages her brood in much the same fashion; only she carries her eggs beneath her body instead of on her back like her amphibious rival. When spawning time approaches, and Aspredo’s fancy lightly turns to thoughts of love, the lower side of her trunk begins to assume, by anticipation, a soft and spongy texture, honeycombed with pits, between which are arranged little spiky protuberances. After laying her eggs, the mother lies flat upon them on the river bottom, and presses them into the spongy skin, where they remain safely attached until they hatch out and begin to manage for themselves in life. It is curious that the only two creatures on earth which have hit out independently this original mode of providing for their offspring should both be citizens of Guiana, where the rivers and marshes must probably harbour some special danger to be thus avoided, not found in equal intensity in other fresh waters.

A prettily marked fish of the Indian Ocean, allied, though not very closely, to the pipe fishes, has also the distinction of handing over the young to the care of the mother instead of the father. Its name is Solenostoma (I regret that no more popular title exists), and it has a pouch, formed in this case by a pair of long broad fins, within which the eggs are attached by interlacing threads that push out from the body. Probably in this instance nutriment is actually provided through these threads for the use of the embryo, in which case we must regard the mechanism as very closely analogous indeed to that which obtains among mammals.

Some few fish, indeed, are truly viviparous; among them certain blennies and carps, in which the eggs hatch out entirely within the body of the mother. One of the most interesting of these divergent types is the common Californian and Mexican silver-fish, an inhabitant of the bays and inlets of sub-tropical America. Its chief peculiarity and title to fame lies in the extreme bigness of its young at birth. The full-grown fish runs to about ten inches in length, fisherman’s scale, while the fry measure as much as three inches apiece; so that they lie, as Professor Seeley somewhat forcibly expresses it, ‘packed in the body of the parent as close as herrings in a barrel.’ This strange habit of retaining the eggs till after they have hatched out is not peculiar to fish among egg-laying animals, for the common little brown English lizard is similarly viviparous, though most of its relatives elsewhere deposit their eggs to be hatched by the heat of the sun in earth or sandbanks.