INFANCY OF CRABS AND CATERPILLARS 255 



hangs itself up by its hind-legs, and puts a silken cord 

 around its body to sustain its weight during the long 

 months it must pass absolutely incapable of movement, 

 performs these acts but once, and perfectly. And the 

 same is true in the case of the more marvellous silk- 

 spinning feats. The cocoon of the silkworm moth, 

 or of the emperor moth, with its marvellous exit, is the 

 work, so to speak, of an untried, unpractised amateur, 

 but it is performed without hesitation, and without 

 mistake. Even when we ascribe these acts, performed 

 but once in a lifetime, by isolated individuals which have 

 never known their parents, and can therefore never have 

 received instruction, to " Natural Selection " acting 

 during thousands of years on millions of individuals, 

 and weeding out the bunglers, we are still far from 

 understanding how, and why, these varied means to 

 attain the same end came to be. And we shall pro- 

 bably fail to penetrate these mysteries to the end of 

 time. 



Alfred Russel Wallace, years ago, strove to show that 

 birds built their nests by imitation : that when the 

 time came for a bird to build its first nest it was guided, 

 in its choice of materials and in the application thereof, 

 by the memory of the nursery in which it was reared. 

 And failing this, then the untried youngster mated with 

 a bird of riper experience ! But what need for such an 

 explanation ? Those who have reared young birds from 

 the nest know that, even when an individual has been 

 brought up in an environment where contact with its 

 own, or any other species, is impossible, yet that youngster 

 wiU in due course perform all the acts common to its 

 tribe perfectly — its note, its song, its mode of bathing, 

 its peculiarities of flight, and finally, its particular mode 



