60 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



side and several bands of muscle are developing in the mesoblast. 

 Two deep grooves give form to what may be called the rudimentary 

 tongue (tn). In both jaws one or two tooth rudiments (to) may 

 be distinguished as small invaginations of ectoderm. 



Stage XXI 



Figure 24 (Plate XXII) 



In this stage the curvature of the body and tail is less marked 

 than was seen in the last surface view. The body has increased 

 greatlv in size, so that the size of the head is relatively not so great. 

 The size of the eye in relation to that of the head is much diminished 

 also. The five anterior and four posterior digits are well formed, 

 and their claws are of considerable size, though of course not present 

 on all the digits. The outlines of scales may be traced from the 

 tip of the tail to the skull ; they are especially prominent along the 

 dorsal profile. The skin is just beginning to show traces of pig- 

 ment, which is, however, not shown in the photograph. The umbil- 

 ical stalk is seen projecting with a loop of the intestine from the ab- 

 dominal wall ; this is shown more clearly in the next stage. The 

 embryo now begins to exhibit some of the external characteristics 

 of the adult alligator. 



Stage XXII 



Figure 25 (Plate XXI II) 



This embryo needs no particular description. It has reached in 

 its external appearance practically the adult condition, although 

 there is still considerable yolk (not shown in the figure) to be ab- 

 sorbed, and the embryo would not have hatched for many days. 

 Pigmentation, begun in the last stage, is now complete. The umbil- 

 ical stalk is clearly seen projecting from a large opening in the body 

 wall. The long loop of the intestine that extends down into the 

 yolk sac is here evident, and it is hard to understand how it can all 

 be drawn up into the body cavity when the umbilical stalk is with- 

 drawn. No sharp shell-tooth at the tip of the snout, such as is 

 described by Voeltzkow (18) in the crocodile, is here seen. 



Stage XXIII 



Figi-re 26 (Plate XXIII) 



This figure shows the relative sizes of the just-hatched alligator 

 and the egg from which it came. It also shows the position of the 

 young alligator in the egg, half of the shell having been removed for 



