Embryonic Development of the Crocodile. 71 



fully removing the shell-membrane, the entire o.^^ may be 

 taken in the hand, rolled about, examined from every side, 

 and even allowed to slide from one hand into the other without 

 colla2)sing. 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 S. F. Clarke in stating that the Qgg 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 &g^ 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 doino' without daraa":ino; 

 the albumen ; tlien, turning the eg^ 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-raicroscope. 

 In spite of every precaution all my trouble was often thrown 

 away. 



It is stated by S. 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 Crocodiliis 

 niloticus, since an expansion of the zone is found even in bad 

 eggs, in which the embryo has perished. Eggs 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 unfortu- 

 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 

 1 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. 



