THE DARWINIAN THEORY 



Loligo, one of the higher Cephalopoda, showing development of eye. 



o, Optic nerve and ganglion ; //, Nerve layer of retina ; /, Lens ; i, Iris ; 

 c, Cornea ; p, Pigment layer of retina ; s, Layer of sensory cells. 



A. — First stage ; a simple pit in the skin. This corresponds to the adult 

 condition in Patella. 

 B. — Narrowing of mouth of pit, corresponding to Haliotis. 

 C. — Closing of pit, and formation of lens, corresponding to Fissurella. 

 D. — Formation of iris. 

 E. — Adult condition. 

 F. — Figure of adult Loligo. 



