Proteus of the Carniola caverns,[58] with its external breathing gills.—(Adapted from Brehm.)
Have these double-lived creatures, then, such a great advantage over real water animals, or how can we account for their having adopted this strange life? If we only look upon them as they are now, we can scarcely call them particularly successful, compared to other animals. For though there are plenty of them, yet they are comparatively small and insignificant; and when we find large ones like the gigantic salamander of Japan, they are sluggish and feeble. Look at the common newts, or water-salamanders of our ponds, with their weak crawling limbs, as they wander round the edges of a pond, feeding on water-insects and tadpoles, the male with his crested back, the smooth mother, and the young eft-tadpole with its branching tufted gills ([Fig. 16]). They are much less active than the frog, for they never lose their tails, and they come less often out of the water, although they are true air-breathing animals. Then, when we go to other countries, there is the Proteus ([Fig. 17]), that curious half-transparent newt, with a round body and tiny helpless legs, which lives in eternal darkness in the still underground pools of the Carniola caverns near Adelsberg. He has become well fitted for his dismal life, for his tiny eyes are grown over with skin, and he never loses the feathery gills on each side of his neck, but lives like a tadpole all his life, although he has true lungs. Again, in America we have the Siren, with its long snake-like body, and only front legs, with which it cannot walk. It, too, keeps its gills as it wanders about the stagnant waters of South Carolina, feeding on worms and insects. Then in the Mexican lakes there are the curious Axolotls, which also wear outside gills, as a rule, all their lives, and fathers, mothers, and children remain breathing in the water together, although they have real lungs. But about twenty years ago, some of those axolotls, which were kept in the Jardin des Plantes in Paris lost their gills, came out upon the land, and astonished people by becoming true land salamanders, like some already well known and called Amblystomes, breathing only with their lungs. It was difficult for some time to make the world believe that grown-up water-breathing creatures which could lay eggs were able to turn into other creatures without gills. But at last a lady, Fraulein Marie von Chauvin, took some axolotls when they were full-grown, and kept them on land in wet moss, washing and feeding them every day, and thus succeeded in teaching them to breathe air, so that their gills shrivelled up and disappeared. Then there could no longer be any doubt that the axolotl is only the lower water-form of the amblystoma, which in the Mexican lakes, owing to the increased dryness of the surrounding country, has lost the habit of coming out on to the land, and remains in the water with its little ones all its life; but which, when brought to a moist climate where it can breathe comfortably on land, sometimes returns to its old double life.
Fig. 18.
Axolotl, a creature living and breeding for generations in the water. Amblystoma coming out of the water,—an axolotl which has lost the gills and acquired lungs.
We have, in fact, in Europe real land salamanders, which live in cool damp places, looking like lumpy soft-skinned lizards, but going down to the water to lay their eggs, that their little ones may go through their tadpole life—and one of these, the black salamander,[59] which lives high up in the mountains of Germany, France, and Switzerland, does not even go to the water, but carries the young tadpoles in her body till they can breathe air and run alone; and yet they are still true amphibia, for if they are taken out of their mother and put in water, they go through all their changes like common efts and newts.
Lastly, there is a strange group of legless creatures called Cæcilians, which have taken refuge underground, burrowing like worms, though they are true amphibians and their young have gills in their babyhood hidden under a slit in the neck. These cæcilians are the only amphibians which have scales something like fishes, yet they never live in the water, but in the marshy ground of tropical countries, feeding on worms and insects.
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Now when we think that these sluggish newts, and salamanders, and cæcilians, with their more nimble but comparatively unprotected relations, the frogs, are all the amphibians now living, we cannot but wonder how Life came to produce such a feeble set of creatures to fight the battle of existence.