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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 
