326 



THE EYE IN EVOLUTION 



Fig. 385. — The Eye of Asableps in Vertical Section. 



The immense cornea (to the left) occupies 2/5ths of the surface of the 

 globe and is bisected horizontally across the middle. Internal to the bisection 

 is seen the part of the iris which spans the anterior chamber transversely to 

 create the two j^upils, the upper for aerial, the lower for aquatic vision. In 

 the lower part of the choroid is seen the huge choroidal gland lying between 

 the detached retina and the sclera (H. Arruga). 



STALKED EYES 



In a few Teleosteans the eyes are set prominently on stalks. An 

 example of this is the mud-skipper, Periophthalmus, found in the 

 tropical swamps of Asia, Africa and Poljmesia, which skips upon the 

 mud on its stiff f)ectoral fins seeking insects (Fig. 386). The eyes are 

 retractile and can be withdrawn for protection when they are covered 

 by puckered skin-folds ; they are raised by a hammock formed by a 

 crossing of the inferior rectus and inferior oblique muscles. When 



FiG.^3S6. — The Mljd-skipper, Fejuophihalmus. 



The water-line cuts the head of the fish just beneath the eyes ; the 

 cor:. ,il reflex is seen reflected immediately underneath on the surface of the 

 wat nhotograph by Michael Soley). 



