DEVELOPMENT OF GALLUS 



209 



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'It 



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B 



Fig. 97. — Gallus : embryo chick after 36 hours' incubation seen by trans- 

 mitted light, A from the dorsal, B from the ventral side. (After Jenkinson.) 



The heart is beginning to bend to the right, and the amniotic folds are 

 covering over the head, af, amniotic fold ; as, auditory sac ; ov, optic 

 vesicle; va, vitelline artery. Other letters as Figs. 90, 91, and 93. 



up from the extra-embryonic part of the blastoderm. This 

 fold extends backwards, and soon covers over the head. It 

 now continues growing backwards by the upgrowth of folds 



p 



