No. 2.] EMBRYOLOGY OF THE AMERICAN ALLIGATOR. 199 



W. K. Parker has called attention to the important fact of a 

 considerable reduction in the number of body segments that 

 are found in the embryos of CJielone viridis about 15 mm. 

 long. They have fifteen cervical, twelve dorso-lumbo-sacral, 

 and twenty-four caudal, — fifty-one in all ; while the adult has 

 only eight cervical, a loss of seven, and twenty-one caudal, a 

 loss of three. Thus there are fifty-one in the embryo and but 

 forty-one in the adult. In the alligator I have found no reduc- 

 tion ; there are thirty-five caudal and twenty-six in front of the 

 caudal in both embryo and adult. 



Summary. 



I. The eggs, to the number of about thirty, are deposited in 

 June in large nests of dead leaves, twigs, grass, and humus, 

 built on the ground close to a stream or pool. 



II. There appears on each egg, soon after it is laid, a trans- 

 verse median belt or zone of slightly different color tone from 

 the remainder ; it has a more chalk-white color than the rest. 

 This belt increases in width with the growth of the embryo, 

 but never extends to the ends of the egg. This change of color 

 is mainly due to a change in the shell membrane. 



III. The embryo usually lies at first toward one pole of the 

 egg, where it has the protection of the large mass of thick 

 white ; later it moves over to a lateral position, and the chalk- 

 white belt is developed around it. More perfect respiration is 

 then needed, and is then readily effected in its new position. 

 The change in the median belt of the shell membrane is appar- 

 ently a drying of that part, and I suggest that it is to still 

 farther facilitate the work of respiration. 



IV. The formation of the anterior portion of the neural folds, 

 the cephalic part, is by a median backward folding on the 

 dorsal side, of a thickened part of the head-fold ; this median 

 fold separates at its apex, each arm uniting with the medullary 

 fold of its respective side. 



V. Tracing the intestine forward from the cloaca, it leaves 

 the body and passes out to become attached to the yolk-sac ; 

 following the intestine backward from the stomach, it also passes 

 out of the body, and is attached to the yolk-sac by the side of 

 the posterior part of the intestine. 



