The Development of the Alligator 335 
unopened egg is due chiefly to stains produced by 
the decayed vegetation of the nest. At hatching 
the young alligator is about 20 cm. long, nearly 
three times the length of the egg; but the tail is so 
compressed that, though it makes up about half 
of the length of the animal, it takes up very little 
room in the egg. 
SUMMARY 
Owing to the fact that the embryo may undergo 
considerable development before the egg is laid, 
and also to the unusual difficulty of removing 
the very young embryos, the earlier stages of 
development are very difficult to obtain. 
The mesoderm seems to be derived chiefly by 
proliferation from the entoderm, in which way all 
of that anterior to the blastopore arises. Posterior 
to the blastopore the mesoderm is proliferated 
from the lower side of the ectoderm in the usual 
way. No distinction can be made between the 
mesoderm derived from the ectoderm and that 
derived from the entoderm. 
The ectoderm shows during the earlier stages a 
very great increase in thickness along the median 
longitudinal axis of the embryo. 
The notochord is apparently of entodermal ori- 
gin, though in the posterior regions, where the 
germ layers are continuous with each other, it is 
difficult to decide with certainty. 
