144 



THE EYE IN EVOLUTION 



Figs. 113 and 114. — The Eye of a Typical Cephalopod. 



e 



Fig. 113. 



Invaginated epithelium forms the optic vesicle (a) lined by the retina (b), 

 the posterior layer of the " ciliary body " (c), and the posterior part of the 

 lens (d). The surface epithehum i'orms the cornea (e), the anterior part of the 

 ciliary body (/ ), the iris (t), and the anterior part of the lens (g), a hole (h) 

 being left at the point of invagination. The eye is surrounded by a carti- 

 laginous orbit, formed by an anterior cartilage (k), an equatorial cartilage (I), 

 and an orbital cartilage {m). n is the optic nerve. 



Fig. 



— The eye of Octopus vulgaris (specimen from J. Z. Young). 



