144 EDWARD MCCRADY, JR. 



patent into the cloaca in stage 30, and the mesonephros gives 

 every indication of being functional in stage 31. Somites are 

 still forming in the tail. Auricular appendages are forming 

 on the heart. 



XII. THE TWELFTH DAY. Stages 32 and 33 



The first half of the twelfth day 



Stage 32. External distinctive features. The veins of the 

 liver and mesonephros. The thoracic duct and the jugular 

 lymph sacs. The adrenal cortex. The foramen ovale. The 

 subintestinal vein. Changes in the branchial pouches. 

 Changes in the digestive tract. Miscellaneous details. 



Fig. 46 Photographs of external views of stage 32. A shows a ventral view of 

 16173 with all extra-embryonic membranes removed. B shows a lateral view of the 

 same specimen. C shows 16174 with the allantois still attached and partly 

 dissected. 



External distinctive features. Stage 32 is distinguished 

 from stage 31 by having the diameter of the allantois approxi- 

 mately two-thirds the length of the body (instead of one- 

 third) ; by the hindlimb being a club instead of a bud; by 

 having definite digital buds on the f orelimb instead of ridges ; 

 by having the ventral thoracic wall opaque instead of trans- 

 parent ; and by having the interval between the first and sixth 

 auricular tubercles very much enlarged. It is distinguished 

 from stage 33 by the absence of the upper eyelid folds, the 

 smaller size of the allantois, and by the hindlimb being a club, 

 not a paddle. 



