MORPHOLOGY OF ANIMALS 



lens and in front of the retina is filled with vitreous humor 

 (Fig. 29, A). 



The compound eye is another type found chiefly among 

 arthropods. It consists of a large number of closely packed 

 single eyes or ommatidia^ each of which is surrounded by pig- 

 ment and is optically isolated from the others. Each omma- 

 tidium consists of (1) a polygonal cornea at the surface, 

 (2) a crystalline cone below this, and (3) the retinula or 

 group of retinal cells which are connected with nerve fibres. 

 The cornea and crystalline cone are refractive and serve in 

 the capacity of a lens, while the retinula alone is the sensory 

 element (Fig. 29, B). 



A summary of the Morphology of Animals is given in the 

 appended Table. 



1:85 3 



