THE EVOLUTION OF INSTINCT 125 



the results of experiment? To anyone who has made any 

 first hand study of lepidopteran psychology the supposition 

 that the ingenious mechanical devices shown hi the cocoon 

 were hit upon as the result of a series of experiments is 

 about as probable as that a cat would be able to comprehend 

 the differential calculus. Yet we read such phrases as "such 

 calculation, " "what wonderful contrivance," applied to such 

 performances by some of the foremost students of animal 

 psychology a couple of decades ago. How absurd they all 

 seem now ! To be able to improve a habit there must be an 

 opportunity for repeating the action. Caterpillars might 

 be supposed, by the mere act of once constructing a cocoon 

 to have adapted their organization to this operation, and 

 we might suppose that this modification affects the germ 

 cells so that the next generation spins with somewhat 

 greater facility. But caterpillars which constructed their 

 cocoons badly would have no opportunity to improve, and 

 their bad methods would be handed on, and confirmed 

 more and more in then- badness. 



After the moth emerges from the cocoon she soon deposits 

 her eggs upon a species of plant which affords suitable food 

 for the larvaB. How did the moth come to have this instinct? 

 Can any one believe that the moth watched the results of 

 laying eggs on different kinds of plants and formed the 

 habit of ovipositing on those upon which the larvae happened 

 to thrive? 



Many of the most complex instincts of insects are in re- 

 lation to constructing some sort of protective dwelling for 

 the winter and in making provision for their progeny, and 

 in neither of these cases is there, hi most forms, room for im- 

 provement through profiting by failures. Protective dwel- 

 lings are usually made but once, and in providing for the 

 young there is usually no opportunity for the parent to 



