146 SECRETS OF ANIMAL LIFE 



and in consequence the period of embryonic de- 

 velopment has been relatively shortened or con- 

 densed. The cock that crows in the morn is, on 

 the whole, except in brain, as complex a creature 

 as the cow that tosses the dog, but the chick breaks 

 its way out of the egg after three weeks of incuba- 

 tion, whereas the calf is carried by the cow for 

 about nine months of antenatal life. In the 

 contrast between the callow nestling type, which 

 corresponds to prolonged infancy, and the preco- 

 cious chick type, which corresponds to abbreviated 

 infancy, we have another familiar illustration of the 

 elasticity of the curve of life. How striking is the 

 case of the Mound-Builders, where the mother-birds 

 have evaded brooding and where the young, hatched 

 within the heap of fermenting vegetation, are able 

 to fly right away. The great majority of fishes are 

 oviparous, with both embryonic and larval phases 

 in the water. In this there are great risks and the 

 juvenile mortality is enormous. Yet, as there are 

 plenty of fry to spare, most species of modern fishes 

 continue to prosper. But how vivid is the contrast 

 between their life-curve and that of the whale, with 

 a single calf slowly developing within the mother 

 and born into the sea a fully-formed and richly 

 endowed cetacean. Just as there are plants which 

 remain for life like half-opened buds, and others 

 which flower before they leaf, and so forth, so there 

 are animals which have a long youth and others a 

 long maturity, some that are born old and others 

 that die young; some which break down suddenly 



