STRUCTURE OF FIFTY-HOUR CHICKS 



97 



are also termed secondary optic vesicles in distinction to prim- 

 ary optic vesicles, as they are called before the invagination. 

 The formerly capacious lumen of the primary optic vesicle is 



vikceral furrow I 



sero-amniotic 

 cavity 



auditory vesicle 



mandibular arch 

 aortic arch 

 dorsal aorta 



pharynx 



myelencephalon 



-amniotic cavity 

 mesocoele 

 ventral aorta 



lens 



sensory layer of retina 

 pigment layer of retina 



diencephalon 



fore-gut 



^^ intra-embryonic coelom 



dorsal mesocardium 

 sero-amniotic raphe 



endocardium of 

 bulbo-conus arteriosus 

 epi-myocardium of 

 ventricle 



somatopleure 

 splanchnopleure 



vitelline vessels 

 extra-embryonic coelom 



atriimi 



neural crest 



dorsal aorta 



post, cardinal v. 



D 



extra-embryonic coelom' 



intra-embryonic coelom 

 omphalomesenteric 



lateral amniotic fold 

 amnion 

 serosa 



mesonephric duct 

 mesonephric tubule 

 mid-gut 



somite 



vitelline vessels 



mesonephric duct 



mesonephric tubvle 



post, cardinal v. 

 dorsal aorta 



Fig. 36. — Diagrams of transverse sections of 55-hour (30-somite) chick. The 

 location of the sections is indicated on an outline sketch of the entire embryo. 



practically obliterated in the formation of the optic cup. What 



remains of the primary opticoele is now but a narrow space be- 



7 



