274 The Alligator and Its Allies 
Body torsion has begun (Fig. 12), so that the 
anterior third of the embryo now lies on its right 
side, while the rest of the body is still dorsal side 
up. The direction of body torsion does not seem 
to be as definite as it is in the chick, some alligator 
embryos turning to the right side, others to the left. 
Clarke has illustrated this fact in his alligator 
figures. He says (17) that embryos lie ‘‘more 
frequently on the left, but often on the right side.” 
The head is distinctly retort-shaped, and at the 
side of the forebrain (v’) a small crescentic thicken- 
ing is the optic vesicle (e). The auditory vesicle, 
though of considerable size, does not show in this 
surface view. The head-fold (k) extends for about 
one third the length of the entire embryo, though 
its exact limit is difficult to determine in surface 
view. There is no sign of a tail-fold. 
About seventeen pairs of somites are present. 
The amnion extends over the anterior two thirds 
of the embryo. 
The above-mentioned increase in the diameter of 
this embryo over that of the preceding is evident 
when the first two transverse sections of this stage 
are compared with the corresponding sections of 
the earlier stage; in the middle and posterior re- 
gions there is not very much difference in size. 
Figure 12a passes through the region of the fore- 
brain. This end of the embryo lies on its side, as 
was noted above and as may be recognized from 
the relative positions of the head and the overlying 
