No. 6. Pipe-Fish.
No. 7. Pouch of Pipe-Fish.
The sea-horses and many other fish have similar pouches; but, oddly enough, in every case it is the male fish which bears it, and which undertakes the arduous duty of nurse for his infant offspring.
A few female fish, on the other hand, even hatch the eggs within their own bodies, and so apparently bring forth their young alive, like the English lizard among reptiles. This, however, is far from a common case: indeed, in an immense number of instances, neither parent pays the slightest attention to the eggs after they are once laid and got rid of: the spawn is left to lie on the bottom and be eaten or spared as chance directs, while the young fry have to take care of themselves, without the aid of parental advice and education. But exceptions occur where both parents show signs of realizing the responsibilities of their position. In some little South American river fish, for instance, the father and mother together build a nest of dead leaves for the spawn, and watch over it in unison until the young are hatched. This case is exactly analogous to that of the doves among birds: I may add that wherever such instances occur they always seem to be accompanied by a markedly gentle and affectionate nature. Brilliantly-coloured fighting polygamous fishes are fierce and cruel: monogamous and faithful animals are seldom bright-hued, but they mate for life and are usually remarkable for their domestic felicity. The doves and love-birds are familiar instances.
Frogs are very closely allied to fish: indeed, one may almost say that every frog begins life as a fish, limbless, gill-bearing, and aquatic, and ends it as something very like a reptile, four-legged, lung-bearing, and more or less terrestrial. For the tadpole is practically in all essentials a fish. It is not odd, therefore, to find that certain frogs reproduce, in a very marked manner, the fatherly traits of their fish-like ancestors. There is a common kind of frog in France, Belgium, and Switzerland, which does not extend to England, but which closely recalls the habits of the stickleback and the pipe-fish. Among these eminently moral amphibians, it is the father, not the mother, who takes entire charge of the family. The female lays her spawn in the shape of long strings or rolls, looking at first sight like slimy necklaces. I have seen them as much as a couple of yards long, lying loose on the grass where the frog lays them. As soon as she has deposited them, however, the father frog hops up, twists the garlands dexterously in loose festoons round his legs and thighs, and then retires with his precious burden to some hole in the bank of his native pond, where he lurks in seclusion till the eggs develop. Frogs do not need frequent doses of food—their meals are often few and far between—and during the six or eight weeks that the eggs take to mature the father probably eats very little, though he may possibly sally forth at night, unobserved, in search of provender. At the end of that time the devoted parent, foreseeing developments, takes to the water once more, so that the tadpoles may be hatched in their proper element. I may add that this frog is a great musician in the breeding season, but that as soon as the tadpoles are hatched out he loses his voice entirely, and does not recover his manly croak till the succeeding spring. This is also the case with the song of many birds, the crest of the newt, the plumes of certain highly-decorated trogons and nightjars, and, roughly speaking, the decorative and attractive features of the male sex in general. Such features are given them during the mating period as allurements for their consorts: they disappear, for the time at least, like a ball-dress after a ball, as soon as no immediate use can any longer be made of them.
Pouched Frog.
Some American tree-frogs, on the other hand, imitate rather the motherly Solenostoma than the fatherly instincts of the pipe-fish or the stickleback. These pretty little creatures have a pouch like the kangaroo, but in their case (as in the kangaroo’s) it is the female who bears it. Within this safe receptacle the eggs are placed by the male, who pushes them in with his hind feet; and they not only undergo their hatching in the pouch, but also pass through their whole tadpole development in the same place. Owing to the care which is thus extended to the eggs and young, these advanced tree-frogs are enabled to lay only about a dozen to fifteen eggs at a time, instead of the countless hundreds often produced by many of their relations.