THE 



PRIMITIVE STREAK AND NOTOCHORDAL 

 CANAL IN CHELONIA.* 



By GERTRUDE CROTTY DAVENPORT. 



CONTENTS. 



PAGE 



I. Collection, Preparation, and Preservation of the Embryos . . i 

 II. Scope of the Paper 4 



III. Description of the Notochordal Invagination 5 



1. Chelydra serpentina 5 



a. Notochordal Canal unbroken 5 



b. Its Length 7 



c. Method of its Formation 7 



2. Chrysemys picta and Ozotheca odorata 8 



a. Breaking througii of the Floor of the Notochordal Canal ... 8 



b. Width and Length of the Notochordal Canal 9 



c. Method of its Formation 11 



IV. Primitive Streak and Dorsal Notochordal Opening 16 



1. The Concavity of the Crescentic Opening is directed anteriad ... 16 



a. Chelydra serpentina 17 



b. Chelopus insculptus 29 



2. The Concavity of the Crescentic Opening is directed posteriad ... 31 



a. Chelydra serpentina 31 



b. Ozotheca odorata 33 



3. Concerning the so called Plug 34 



V. Regression of the Neurenteric Canal along the Streak ... 40 



VI. Summary 45 



Bibliography 47 



Explanation of Plates 54 



I. Collection, Preparation, and Preservation of the 



Embryos. 



ALL the embryos figured and described in this paper were 

 collected in the neighborhood of Boston. The eggs were 

 taken from the nests at different periods after deposition. In some 

 instances the surface of the freshly disturbed soil had not had time 



* Contributions from the Zoological Laboratory of the Museum of Comparative Zoology at 

 Harvard College, under the Direction of E. L. Mark. No. LXVIL 



I 



