CHAP. VI The Domestic Life of Animals iii 



his mate, winds them round his hind-legs, and retires into a 

 hole, whence, after a fortnight or so, he betakes himself to the 

 water, there to be relieved by the speedy hatching of his 

 precious burden. Even quainter is the habit of the male of 

 a Chilian irQg{Rkinoderma dar'winii),vi\io keeps the eggs and 

 the young in a pouch near the larynx, turning a resonating 

 sac in a most matter-of-fact way into a cradle. He is some- 

 what leaner after it is all over. It is interesting to notice 

 how similar forms and habits recur among animals of dif- 

 ferent kinds, like the theme in some musical compositions. 

 The spiral form of shell common in the simple chalk-forming 

 f'oraminifers recurs in the pearly nautilus ; the eye of a 

 fish is practically like that of many a cuttle, though the 

 two are made in quite different ways ; and an extraordinary 

 development of paternal care may signalise animals so 

 distinct as sea-spider, stickleback, and frog. 



But we must not be unfair to the female amphibians. 

 Without doubt most of them are willing to be quickly rid 

 of their eggs or young, and as these are usually very 

 numerous, the mortality in the pools is of little moment. 

 In some cases, however, water-pools are less available 

 than in Britain, and then we find adaptations securing the 

 welfare of the young. The black salamander of the Alps, 

 living at elevations where pools are rare, retains her twin 

 offspring until more than half of the tadpole life is past. 

 They breathe and feed in a marvellous way within the 

 body of the mother, and are born as lung-breathers. In 

 the case of the Surinam Toad (fipd), the male places half 

 a hundred eggs on the back of the female, where they 

 become surrounded by small pockets of skin, from which 

 the young toads writhe out fully formed. In two other 

 cases {Nototrema and Notodelphys), the above somewhat 

 expensive adaptation, which involves a great destruction 

 of skin, is replaced by a dorsal pouch in which the eggs 

 hatch, an arrangement dimly suggestive of the pouch of 

 kangaroos and other marsupial mammals. 



Fishes and amphibians are linked closely by their likeness 

 in structure, and, as we have seen, they are somewhat alike 

 in parental habits ; but how great is the contrast between 



