Embryonic Development of the Crocodile. 69 
The fact that sounds are produced by the young in the egg 
was unknown to anybody here. The natives laughed at me 
when I spoke about it, until by listening they were convinced 
of their mistake. The sounds are produced with the mouth 
closed, apparently by powerful contraction of the ventral 
muscles, much as we make a noise when hiccoughing. The 
sound, too, is similar. 
When the young animals have emerged the old crocodile 
goes with them to the water. My taxidermist, a thoroughly 
trustworthy man, who has previously travelled with Dr. 
Fischer, told me that a short time before he had seen a large 
crocodile with a tribe of about twenty young ones travelling 
over a stretch of sand to the water. He stated that the old 
one was remarkably savage. That the just-hatched young 
are able, without help from the mother, to break through the 
superincumbent layer of sand I believe that I am entitled, 
according to the experiments which I have made, to deny as 
emphatically as possible. Of the eggs which were covered 
with a layer of sand about 14 to 2 feet in depth it is true that 
a few showed feeble attempts on the part of the young to 
escape, in that the shell was broken at one point, while some- 
times the young animals had protruded the tip of the snout; 
but they had invariably perished, probably from want of air. 
The eggs which were only lightly covered with sand pre- 
sented no difficulties to the young in escaping. 
The process of hatching is preceded by a change in the 
position of the embryo, with partial destruction of the embry- 
onic membranes, so that the tip of the snout of the young 
animal now comes into contact with one end of the egg; at 
any rate this was the position of all embryos which were 
ready to emerge. The piercing of the egg-shell is effected by 
the mechanical operation of the egg-tooth, which is also found 
in young birds,. The rudiments of this tooth may be detected 
at a very early stage, at the period at which the young croco- 
diles begin to assume their definite shape, therefore when the 
embryos are about one and a half to two months old. In the 
just-hatched young it appears as a tooth about $ to ¢ millim. 
in length, terminating in two points; the movements of the 
animal cause it to act precisely like a gimlet. In crocodiles 
a fortnight old it was still distinctly recognizable. On the 
perforation of the egg the embryonic fluid escapes and_pro- 
duces a softening of the adjacent parts of the shell, and the 
young animal forces itself backwards through the narrow 
cleft. A specimen which was watched from the moment it 
pierced the egg-shell took about two hours to completely 
emerge. As the animal forces itself through the narrow hole 
