180 THE SENSES AND SENSE-ORGANS OV INSECTS. 



may to the bnttcrfly bo made musical with a symphony of 

 HoLar radiance. I do not for ono moment assert that this is 

 so. My puiposo is merely to sliow tliat thoi-o may be " per- 

 manent possibilities of sensation " to tlio insect of which wo 

 duller folk may only sometimes dream, with a sort of night- 

 mare consciousness, the while, that folk yet duller still are 

 laughing at us for our pains. 



The speaker passed in review the more recent advances 

 in our knowledge of the morphology and physiology of in- 

 sect sense-organs. Concerning the psychology of the subject, 

 he maintained that we could only make more or less improb- 

 able guesses from analogy. 



He pointed out that the important role which sense-hairs 

 or setiB play in organisms enshoathed in chitinous armour ; 

 and compared in this respect insects and their allies the 

 Crustacea. In Fig. 1, A B D (from the writer's Animal 

 Biology, by the kind pei'mission of Messrs. Rivington) tactile, 

 olfactory, and auditory setsB from the crayfish are shown. 



The structure of the .arthropod eye and the principle 

 of arthropod vision was considered. Fig. 1, h] shows a 

 section of the eye of a crayfish, while F is intended diagra- 

 raatically to illustrate the principle of mosaic vision. At a h 

 are a number of transparent rods, separated by pigmented 

 material absorbent of light. They represent the crystalline , 

 cones of B. Ai c d is an arrow placed in front of them. 

 Ate /is a screen placed behind them. Rays of light start 

 in all directions, from any point c of the arrow ; bnt of those 

 only that which passes straight down one of the transparent 

 rods readies the screen. Tliose which pass obliquely into 

 other rods, are absorbed by the pigmented material. 

 Similarly, with rays starting from other points of the arrow. 

 Only thofso which pass straight down ono of the rods reach 



