The Development of the Alligator 233 
quote directly Clarke’s paper in the Journal of 
Morphology (17) in description of these surface 
views. 
STAGE I 
Figures 2-2f (PLates VI., VII.) 
The youngest embryo that we have for descrip- 
tion is shown in Figures 2 and 2a. Of Figure 2 
Clarke says: 
“The limiting line between the opaque and 
pellucid areas is clearly marked, and within the 
latter is a shield-shaped area connected by the nar- 
rower region of the primitive streak with the area 
opaca. The blastopore is already formed near 
the posterior end of the shield. 
“A ventral view of another embryo of the same 
age (Fig. 2a), seen from the ventral side, shows 
that the blastopore extends quite through the 
blastoderm, in an oblique direction downwards 
and forwards, from the dorsal to the ventral side. 
The thickened area of the primitive streak is here 
very prominent. There is, too, the beginning of a 
curved depression at the anterior end of the shield, 
the first formation of the head-fold.”’ 
Transverse sections of this stage are shown in 
Figures 2b-2f. 
Figure 2b, through the anterior region of the 
blastoderm, shows a sharply defined ectoderm (ec) 
which is composed of three or four layers of cells 
