The Development of the Alligator 293 
STAGE XI 
Ficure 14 (PLATE XXI.) 
Only the anterior region of this embryo is shown 
in the figure, which is a ventro-lateral view. While 
there is some change in the general shape and in 
parts of the head, the reason for figuring this 
stage is to show the first gill cleft (g’), which lies 
at an acute angle to the long axis of the neck behind 
the eye (e). The cleft is narrow but sharp and 
distinct in outline; it shows neither in this nor in 
the following stages the branched, Y-shaped out- 
line mentioned by Clarke. 
STAGE XII 
Ficures 15-15f (PLATeEs XXI., XXII.) 
In this stage, also, only the anterior region of the 
embryo is figured in surface view. The shape of 
the head is about the same as in the preceding 
stage, but it is drawn in exact profile. Three 
gill clefts (g*™°) are now present, and are wide and 
distinct. The first cleft, as in the preceding stage, 
lies at an acute angle to the long axis of the pharynx 
and nearly at right angles to the second cleft. The 
third cleft sends a wide branch (g*) toward the 
posterior, as has been described by Clarke, from 
which, or in connection with which according to 
Clarke, the fourth cleft will develop. All three 
clefts may be distinctly seen to open entirely 
