88 THE COCKROACH [CH. Ill 



palps are also in all probability organs of touch and of 

 smell rather than of taste, this latter sense being ap- 

 parently possessed by the margins and walls of the mouth 

 itself. At the posterior end of the body the two cerci are 

 extremely sensitive to touch, and may perhaps act as 

 sentinels in the rear and possibly also have special tactile 

 functions during coitus. 



To what extent the compound eyes are capable of 

 forming a distinct image of surrounding objects we can- 

 not say, but it is evident that they are keenly sensitive 

 to differences of light and shade from the speed with 

 which a cockroach makes for dark corners and crevices 

 when disturbed. That some insects obtain clearly denned 

 visual impressions seems indisputable. I once observed 

 a Brimstone butterfly visiting flowers of the Dog Violet 

 scattered along a bank, and picking out these flowers to 

 the exclusion of all others with great precision, not ap- 

 proaching even other blue flowers that were present. 



No auditory organ has been discovered in the cock- 

 roach, nor is it probable that they are capable of hearing, 

 and in this connexion it is interesting to note that they 

 are likewise incapable of emitting sound. There is a very 

 great diversity among insects in regard to the position 

 and structure of auditory organs and of contrivances for 

 the production of sound. 



Space does not permit us to enter fully into this 

 interesting subject, and it must suffice to deal only with 

 these structures in the grasshoppers, locusts and crickets. 

 The chirrup of the grasshopper is produced, as may easily 

 be observed on any bright day in summer-time, by the 



