2 Primitive Streak and Notochordal Canal in Chelonia. 



to dry. Indeed, in one instance the female — Chelopus insculptus — 

 was found in the act of laying, and the eggs were taken from the 

 uncovered nest. The nest was of the same form as that described 

 by Professor Agassiz ('57, p. 500) for Chelydra serpentina. The 

 perpendicular excavation was about five inches deep. From the 

 bottom of this excavation a chamber extended horizontally for 

 some three or four inches. The female stood over the external 

 opening in such a manner that the axis of her body was parallel to 

 and directly above the horizontal chamber. The blind end of the 

 horizontal chamber pointed anteriad in relation to the axis of her 

 body. During each act of deposition she pressed the cloacal end 

 of the body as far as possible into the perpendicular hole and let 

 the egg fall to the bottom. Then she extended one hind foot into 

 the hole and pushed the egg anteriad into the horizontal chamber. 

 What seemed remarkable to me was the fact that she used the left 

 foot to arrange one egg, then the right foot for the next, and so on 

 alternately for the eight eggs she had to deposit. Did a deposition 

 of the Q.^^ from the right or left oviduct induce this alternation of 

 foot movement? Do the eggs come alternately from the right 

 and the left oviduct .'' 



An effort was made to obtain eggs from females kept in con- 

 finement; but, although males and females were kept in a pen out 

 of doors with sufficient food, — earthworms, — and with water for 

 swimming, no eggs were laid by the end of June. The females 

 were then chloroformed, and unfertilized eggs were found still 

 retained in the oviducts. 



Since all attempts to gain fertilized eggs from captive turtles 

 failed, all the embryos described in this paper were taken from 

 eggs laid by free turtles. Upon removal from the nest, the eggs 

 were packed in moist sand and thus transported to the laboratory. 

 As soon as possible after arrival in Cambridge the embryos were 

 removed from the eggs, not longer than two or three hours after 

 their first discovery. 



During the early stages, as Mitsukuri ('93, p. 230) has already 

 said, the embryo is not yet attached to the shell ; therefore, if pre- 

 caution against desiccation is taken, the eggs may be transported 

 with perfect safety to the embryos. 



In order to remove the embryo, the ^^^ shell was broken and 

 a portion carefully torn away by means of forceps. When a suffi- 

 ciently large opening had been made, the whole contents were 



