INTRODUCTION. 23 



flies, as there are no organs known to serve as receptive 

 elements, and the sounds made by butterflies arc apparently 

 due simply to the rustling of the wings. All motions that 

 look as if j)ossibly meant to convey sound (where none can 

 be detected by the human ear), such as the quivering of 

 the wings in sexual approximation, may be solely to waft 

 emitted odors the more effectivel3\ 



Little can be said or ]oresumed regarding touch of 

 animals whose external parts are all crustaceous; but it is 

 plain that warmth and cold, which deal with the same 

 nervous elements, have decided influences in every stage 

 beyond the Qgg. The ordinary inactivity of caterpillars in 

 the nio-ht can not be laid to the absence of lifrht, for their 

 behavior in darkened apartments is much the same as out 

 of doors; the movements of chrysalids tell the same story; 

 and we know that a measurable amount of movement of 

 the antennae occurs with changing temperature in hiber- 

 nating, practically dormant, butterflies. 



13. Mimicry axd Protective Resemblance. 



Most butterflies when at complete rest close their hind 

 wings back to back and sink the fore wings as far as pos- 

 sible into concealment behind them. The area of these 

 wings then exposed to view is in a very large proportion of 

 butterflies so colored and mottled or marbled as to render 

 the butterfly immensely less conspicuous in its resting- 

 place than if settled with wings expanded or the front pair 

 not mostly concealed; in very many cases so little con- 

 spicuous as to be difficult to detect. Earely are any other 

 parts similarly colored. That this resemblance is protective 

 there can be no doubt, especially in view of its common 

 occurrence. 



There are, however, innumerable instances of special and 

 striking provisions in this direction, of which one of the 



