ARTHROPODAL VISION. 67 



ordinary house-fly (Afusca) are quadrangular. This is true of 

 some of them, but many of them, possibly the greater part, 

 are hexagonal. 



The cornea of the insect eye is lamellar and, under the 

 microscope, fragments will usualh^ show areas near the edges 

 where through exfoliation there are various thicknesses and 

 the foci of the facets of the thinner parts are of course longer 

 than the foci of the corneules which remain intact, and the 

 images obtained through the former are larger. 



The eye of the bee is very hairy in parts, as shown in 

 Plate II, Fig. 7. 



The pigment is often black, but is in many insects highly 

 colored, yellow, green, brown, purple and red being common. 

 In the house-fly it has the rich color of the garnet, which 

 unfortunately cannot be shown in an ordinary photograph, 

 but the microscopical reader is strongly advised to examine 

 this object in the living animal with low powers and in a 

 fresh dissection with higher powers, for the sake of its beauty. 



In conclusion it may be observed that the student who 

 shall undertake further work along these lines must realize 

 that while our own sensory organs present sufficient difficult}^ 

 to the investigator, notwithstanding that his own conscious- 

 ness is a constant and valuable aid to interpretation, there is 

 much greater difficulty in the case of the arthropod where 

 there is marked dissimilarity of structure and where we are 

 necessarily shut out from personal experience. 



Nevertheless he will be richly repaid for his labor though 

 he may be unable to accept any theory of arthropodal vision 

 already proposed or confidently to offer a new one. 



