158 THE HAUNTS OF LIFE 



band, parts of which are elastic, so that they 

 can be stretched out further or shortened down. 

 Thus some animals have a very long embryo 

 period (like Peripatus), others a very long 

 larval period (like May-flies), others a long 

 childhood (like kittens), others a long maturity 

 (like horses). When it is necessary, a part of 

 the life-curve can be, as it were, stretched out 

 in the course of generations man is stretching 

 out his youthful period and another part can 

 be shortened down. Many fresh-water animals 

 have shortened down the riskful juvenile period. 

 A clear example of what we mean may be 

 found in the fresh- water crayfish. It is as high 

 up the genealogical tree as the lobster, and 

 almost as high up as the crab. But while the 

 shore-crab has a long life-history, sketched in 

 our study of the seashore, with one larval stage 

 after another, the young of the fresh-water 

 crayfish is hatched as a miniature of its parent. 

 It is practically identical with its parents, 

 except that the tips of its claws are bent in, the 

 better for gripping the empty egg-shells which 

 are glued to the swimmerets of the mother. It 

 has no larval stages to pass through ; it remains 

 in shelter under its mother's tail until it is able 

 to fend for itself. Indeed, the young crayfishes 



