THE FROG — A REPRESENTATIVE VERTEBRATE 



421 



D 

 Blastocoelei YolK plug-i Archenterom Neural fold — i 



/ N ^J;««^*Blastopor« ^ - •K 



3^ 



r^ 



\ 



^, 



G H I 



Eye pcimoirtJiiun /-Gill primordium Brain rSpina 



I / -— ., Optic L ^-, .^, , [ ^ 



nal cord 



I Nasal t, 



f primordiuTrr ytf^v 



Oredi primorniixiin 



K 



Myotomefi- 



'^lail 



bud Pharynx - 



Liver diverticulum 



"OradsucKcr 

 Moulh-\ I — -K>- 



^Notochord 

 Cloaca 



YolK 



" ^mm^ (^ 



External gills 



yk>u.lh. 



H p 



Figure 21.20. The development of the frog. A, Zygote; B-E, cleavage; F-G, 

 blastula: H-I, late gastrula: J, neural folds: K-L, late embryo; M, early larva; A', opercu- 

 lar folds; O, late larva; P, metamorphosis. (A-H, J-K, M-O, after Shumway; G, 1, L, 

 from Rugh after Huettner; P, after Rugh.) 



