Embryonic Development of the Crocodile. 71 
fully removing the shell-membrane, the entire egg may be 
taken in the hand, rolled about, examined from every side, 
and even allowed to slide from one hand into the other without 
collapsing. The yolk is globular and so large that it reaches 
almost to the long sides of the shell-membrane. The colour 
is somewhat brighter than in the case of the fowl. The 
vitelline membrane is very delicate, but so tough that it is 
possible with a little practice to remove the albumen entirely, 
until finally only the yolk is retained in the hand; the yolk 
then naturally assumes the shape of a round flat cake. 
I must agree with §. F. Clarke in stating that the egg of 
the crocodile is the tenderest and most difficult object to 
manipulate imaginable, since the conditions which have just 
been described apply to perfectly fresh eggs only; subse- 
quently it is only extremely seldom that the egg can be pre- 
pared without injury. I adopted the expedient of first 
removing one half of the egg-shell and then half of the shell- 
membrane, which I succeeded in doing without damaging 
the albumen ; then, turning the egg gently, I searched for 
the embryo ; if I discovered it I opened the albumen and yolk 
by a quick cut with the scissors, and then allowed the embryo 
to slide slowly into a watch-glass; the whole was then lifted 
up, and further manipulated under a dissecting-microscope. 
In spite of every precaution all my trouble was often thrown 
away. 
hie stated by 8. F. Clarke that it is possible to determine 
the position of the embryo from without by the fact that at 
one spot the above-mentioned ring-shaped white zone is 
expanded. This statement is not applicable to Crocodilus 
niloticus, since an expansion of the zone is found even in bad 
eggs, in which the embryo has perished. Hggs which develop 
normally exhibit no trace of change in their external appear- 
ance until the escape of the young animal, but appear pure 
white. 
It would be premature at the present moment to attempt 
to give a review of the entire course of the embryonic develop- 
ment, since my investigations are not yet concluded and will 
need a supplementary examination next year, for untortu- 
nately perfectly new-laid eggs have not come to hand so 
plentifully as might have been wished. 
The youngest embryos observed, about six days old, were 
dumbbell-shaped and 3 millim. in length; the amnion was 
not yet closed. The object is unfortunately so delicate that 
I have not yet succeeded in examining these stages under the 
microscope, and I was obliged to confine myself to preserving 
these as well as the perhaps even younger stages in toto. 
