104 EDWARD MCCRADY, JR. 



In stage 28 that also closes and its location at the time of 

 closure is seen in the reconstruction (fig. 36). The posterior 

 neuropore, however, is very wide in stage 27 (fig. 30, E), and 

 does not close until stage 30. 



The otic cups, though still open, are in late specimens 

 somewhat constricted at the mouth. 



The third gill pouch is now distinct from the posterior 

 complex. 



Comparative data reveal the same set of relations between 

 the different organ systems as that described in connection 

 with earlier stages. As the generalizations based upon the 

 early stages apply equally well to the later ones, detailed com- 

 parisons with other species will be omitted until the discussion 

 of the condition at birth (stage 35). 



The middle of the tenth day 



Stage 28. External distinctive features. The primary 

 lumbar flexure. The mesonephric tubules. The liver di- 

 verticulum. The paracardinal plexus. The veins of the limb 

 .buds. The allantois. Miscellaneous details. 



Fig. 35 Photographs of external views of stage 28. A, ventral view of 16149 

 after removal of non-vascular chorion. B, ventral view of 16154 after removal of 

 all extra-embryonic membranes except anlage of the body stalk. C, lateral view 

 of 16150. D, dorsal view to show amniopore of embryo shown in A. E, ventral 

 view of 16150 before the removal of the area vasculosa. 



External distinctive features. Stage 28 is distinguished ex- 

 ternally from stage 27 by the closure of the otocysts and an- 

 terior neuropore (fig. 35, C and B), and by the fact that the 



