104 



THE DEVELOPMENT OF THE CHICK 



pr.str. 



FIG. 59. Embryo of 7 s from above drawn 

 in balsam with transmitted light, x 30. 



a. c. s., Anterior cerebral suture, ceph. 

 Mes., Cephalic Mesoblast. F. G., Fore-gut. 

 N'ch., Notochord. n. T., Neural tube. op. 

 Ves., Optic vesicle. Pr'a., Proamnion. pr. 

 str., Primitive streak, s 2, s 7, Second and 

 seventh somites. V. o. m., Omphalo-mes- 

 enteric vein. 



