On the Mechanical Conception of Nature. 649 



adapted to these conditions, because every species 

 does not give rise to the necessary colour varia- 

 tions ; those that do, become in this way modified, 

 because they are thus better protected than before. 

 And so it is throughout ; wherever we find pro- 

 tected insects enjoying immunity from foes we see 

 also mimickers, sometimes only single, sometimes 

 several, and generally from very diverse groups of 

 insects, according to the general resemblance 

 which existed before the commencement of the 

 process of adaptation, and to the variations made 

 possible by the physical nature of the species con- 

 cerned. 



In the first essay of the second part of this 

 work it was shown that in certain Lepidopterous 

 larvae a process of adaptation is at the present 

 time still in progress, this depending upon the fact 

 that while the young caterpillar is very well pro- 

 tected by the leaf-green colour of its body, this 

 colour becomes insufficient to conceal the insect 

 as soon as it exceeds the leaf in size. All such 

 caterpillars and there is a whole series of species 

 as they increase in size acquire the habit of 

 concealing themselves on the earth by day, and 

 of feeding only at night. New conditions of life 

 are thus imposed, and these are even com- 

 pulsory, t. e. they could not be abandoned without 

 risking the existence of the species. Now in 

 accordance with these new conditions, some indi- 

 viduals in these species have lost the green colour- 



