The Development of the Alligator 315 
knob contains a distinct cavity (not shown in 
the figure), the myoccel. 
In Figure 17g, owing to the curvature of the body, 
the plane of the section passes through the body 
at three places: through the region of the heart and 
lungs (Fig. 17d), through the region of the posterior 
appendages, and through the tail. In fact, the 
plane of the section represented by each of the 
preceding figures cut the embryo in more than one 
region, but for the sake of simplicity only one 
region was represented in each figure. In the figure 
under discussion only the leg and tail regions have 
been drawn, though the latter region (¢), being cut 
through one of its curves, is seen as an elon- 
gated body with a section of the spinal cord, noto- 
chord, etc., at each end. Both regions shown in 
the figure are enclosed in the same fold (a) of the 
amnion. Of the structures in the dorsal side of the 
larger or more anterior part of this figure nothing 
need be said. The most striking feature of the 
section is the presence of the large posterior leg 
rudiments (pa). As was noted in the preceding 
figure, they are, as usual, merely local enlarge- 
ments or projections of the mesoblast (covered, 
of course, with ectoblast) of the Wolffian ridge. 
They are, as shown in this section and in the sur- 
face view of this stage (Fig. 17), bluntly pointed pro- 
jections from the sides of the body. The anterior 
appendage seems to be slightly more developed 
than the posterior, as was noted in describing the 
