Agassiz on the Embryology of the Turtle. 355 
ment; the bones of the toes becoming very much elongated, and 
the web,—which remains soft among some turtles with moder- 
- ately elongated toes,—is hardened by the development of densely 
ook scales, so that the whole foot is almost as rigid as the 
lade of an oar. About two months before the time they were 
hatched, some young of Chelydra (Chelonura) serpentina, were 
observed to move the head, feet, tail, lower jaw, tongue, and also 
the toes Separately, and to roll the eyes. In a turtle a little older 
than these, the omphalo-meseraic vein runs in a direct line 
through the yolk mass, and joins the exterior boundaries of the 
vascular area at the lower side of the egg. 
By the time the shield has become broadly oval the embryo 
assumes again an erect position in the egg, and t us remains 
tllit is hatched. The embryo of Chelydra serpentina already 
Shows its predaceous propensities, by snapping at everything 
Which touches it. Just before the young were hatck edges 
of the jaws were cut open longitudinally, and disclosed a series 
of small cavities, into each of which, a branch from the maxil- 
lary nerve ran, No doubt these indicate a typical tendency to 
the formation of teeth. When the young is hatching a large 
mass of the yolk sac is still hanging outside of the umbilical 
pPening; but within a few hours it is altogether drawn into the 
: nd occupies a large space in the abdominal cavity. The 
“rculation in the yolk sac at this time is in full tide of operation. 
Externally the allantois withers and falls away, but, within the 
bade turtle, its neck is persistent and becomes the urinary 
adder, : 
The brain at this time does not extend in nearly a straight 
line, as is the case in the adult, but is still considerably bent 
i resents some hitherto 
¢. It is this membrane whic supports the ‘‘ membrana pupil- 
latis” and not the hyaloid membrane as has been claimed for 
‘stology.—A great part of the histology relates to the young 
turtle aes the ‘ae dente hatched. In the formation of nerve 
fibres op tubuli, the olfactory nerve furnished the most conclusive 
Proof that these tubuli originate by the soldering end to end of 
the hervous cells, and the obliteration of the intervening walls 
tthe point of contact. All stages of development were repre- 
Be in a li th par- 
he ere, from cells arranged in a line end to end, with p 
_ ‘Rally absorbed walls, up to those wheré the only indication of 
. 
: 
