124 THE EVOLUTION OF INSTINCT 



the supposed influence of the transmission of acquired 

 characters in the evolution of instinct. The fundamental 

 question is, of course, a biological one, and in whatever way 

 it is decided the psychologist will have to shape his theories 

 accordingly. Opinion among biologists has been setting 

 rather strongly against neo-Lamarckism, and the same 

 tendency is evinced among many writers on animal beha- 

 vior, such as Lloyd Morgan, Forel, Groos, Whitman, Bald- 

 win, and others. The strong resemblance between habits 

 and instincts which has so often been commented upon, 

 naturally disposes one to regard the latter as in some way 

 derived from the former; nevertheless, it is especially in the 

 field of instinct that the Lamarckian theory, which at first 

 seems so plausible, is found upon critical examination to 

 reveal its inadequacy. 



In the insects, where we find so many striking examples 

 of almost pure instinct, there are numerous highly complex 

 instinctive acts which are performed only once in the life- 

 time of the individual. The larva of the promethus moth, 

 for instance, when nearly ready to pupate, spins an elabo- 

 rate cocoon in which it passes the winter. It lines the 

 cocoon with a loose mass of silken threads which will lie 

 next to its body; the outer layer is a firm resistant coat which 

 is admirably adapted to keep out cold and moisture, and at 

 one end, with apparent foresight, there is left an opening 

 filled with loose silk through which the moth may push its 

 way when emerging from the pupal case. Still more re- 

 markable provision is apparently manifested in the way in 

 which the cocoon is attached; it is usually spun against 

 a leaf by which it is partly enclosed, and to guard against 

 falling when the leaf breaks off, a strand of web is spun 

 along the petiole to the twig. How could such a cocoon 

 spinning instinct have arisen? Was it by reflection upon 



