6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 51 



white line, and varies in size from perhaps a square centimeter to 

 one-third the surface of the yolk. 



During the earliest stages of development the embryo is very trans- 

 parent; so that, as there is no fixed place upon the yolk at which it 

 may be expected to occur, it is often very difficult to find. Owing to 

 this transparency, to the extreme delicacy of the embryo, and to the 

 character of the white, the removal of an early embryo from the egg 

 of the alligator is a difficult operation and is accomplished only after 

 some practice. 



The Development of the Embryo 



As the writer has pointed out elsewhere (13), the embryo of the 

 alligator is often of considerable size when the egg is laid. This 

 makes the obtaining of the earliest stages of development a difficult 

 matter ; so that the writer, as has already been said, like S. F. Clarke 

 (5), made three trips to the South in quest of the desired material. 

 Voeltzkow (18) experienced the same difficulty in his work on the 

 crocodile, and made several trips to Africa before he succeeded in 

 obtaining all the desired stages of development. 



To obtain the earliest stages, I watched the newly made nests until 

 the eggs were laid, and in this way a number of eggs w r ere obtained 

 within a very few hours after they had been deposited, and all of 

 these eggs contained embryos of a more or less advanced stage of 

 development. Gravid females were then killed, and the eggs re- 

 moved from the oviducts. These eggs, although removed from a 

 "cold-blooded" animal, generally contained embryos of some size, 

 and only one lot of eggs thus obtained contained undeveloped em- 

 bryos, which embryos refused to develop further in spite of the most 

 careful treatment. Voeltzkow (18) found, in the same way, that the 

 earlier stages of the crocodile were extremely difficult to handle ; so 

 that, in order to obtain the earlier stages, he was reduced to the 

 rather cruel expedient of tying a gravid female and periodically re- 

 moving the eggs from the oviducts through a slit cut in the body 

 wall. 



The older embryos are hardy and bear transportation well, so that 

 it is comparatively easy to obtain the later stages of development. 



For the stages up to the formation of the first four or five somites, 

 I am indebted, as I have already said, to Professor Clarke, and, 

 since I have had opportunity to examine only the sections and not 

 the surface views of these stages, I shall quote directly Clarke's 

 paper in the Journal of Morphology (5) in description of these sur- 

 face views. 



