The Development of the Frog 41 



THE EYE 



The development of the eye can be more 

 easily made out in" the chick than in the frog, 



NS 



M 



FIG. 15. TRANSVERSE SECTION ACROSS THE MIDDLE OF THE 

 EMBRYO SHOWN IN FIG. II, D. (After Marshall.) 



CH, notochord. C/, subnotochordal rod. CM, myocoel. CS, body cav- 

 ity. E, ectoblast. KB, archinephric duct. M, mesoblast. MS, mesoblastc 

 somite. ND, dorsal root of spinal nerve. N S, spinal cord. .S 0, somatopleure. 

 SP, splanchnopleure. T, intestinal region of mesenteron. F, yolk-celJs. 



so that many of the details will be left until 

 the latter part of the book, since the process 

 is essentially the same in both animals. 



The first rudiment of the eye is seen in 



