DEVELOPMENT OF EYE OF SPARROW 



267 



oping eye vertical to the paper and along the line S-S of text- 

 figure 2, C. For the sake of convenience the ectoderm is omitted. 

 The forward projection of the dorsal part, the retardation of the 

 ventral part, and the almost complete obliteration of the primary- 

 optic vesicle are very noticeable. 



ab 



Text fig. 4 Chick of about forty-four hours' incubation, showing the side 

 view of the head, ab, afterbrain ; /g, fore gut; h, heart; tns, mesoblastic somites; 

 nc, notocord; opv, optic vesicle. 



The retardation of growth of the ventral cells prevents the 

 complete closing over or uniting of the ventral border of the 

 optic cup at this stage. This space or groove which is left is 

 the chorioid fissure. It is more clearly understood by examining 

 text-figure 3, B, a section made at right angles to the paper 

 and along the line S-S of text-figure 3, A. The ectoderm is 

 very thin and enables one easily to perceive the lens, the horse- 

 shoe-shaped run of the optic cup (opv), and the wide chorioid 

 fissure below. 



