OUR BEST FEATURES 



surface of the body, but in the vertebrates the 

 paired eyes are essentially an outgrowth of a 

 definite part of the forebrain, only the outer parts 

 of the eye (including the lens and cornea) being 

 contributed by the epithelium; although eventually 



cor^ cor 

 iris 



ei/eiid 



optnv. 



cart/. 



Fig. 94. Eye of Squid (Horizontal Median Section). (From 



Plate, after Hensen.) 



(Prom Allgem. Zool., Gustav Fischer.) 



the brain itself has been derived from the same 



primary outer layer or ectoderm. 



Among all the hosts of invertebrates the paired 



eyes which at first seem to approach the vertebrate 



type most nearly are found in some of the ceph- 



alopod molluscs, especially the squids and 



179 



