Summary. 45 



SUMMARY. 



1. In turtles the notochordal canal is lengthened, in part at 

 least, by the backward migration of its dorsal opening, — the 

 neurenteric canal. 



2. There is evidence that the lumen of the notochordal canal 

 may in some cases be completed anteriad and open towards the 

 yolk ventrally before the dorsal or ectodermal opening is formed. 



3. The lumen of the notochordal canal may be formed as an 

 invagination from the dorsal surface, or by a yielding or disinte- 

 gration of cells within a solid process. 



4. The primitive groove exists on the streak before the horns 

 of the open portion of the blastopore turn backward. 



5 . It may persist on the streak for some time after the horns of 

 the open portion of the blastopore bend backward, and it is later 

 obliterated. 



6. The size of the open portion of the blastopore gradually 

 diminishes. 



7. The open portion of the blastopore migrates backward along 

 the streak by a process of fusion of the halves of its anterior lip, 

 and by a reopening of the halves of its posterior lip. 



8. The anterior lip for a time fuses more rapidly than the 

 posterior lip reopens, and thus the size of the open portion of the 

 blastopore, or neurenteric canal, is diminished. 



9. On account of this rapid fusion of the anterior lip and the 

 tardy reopening of the posterior lip, a portion of the posterior lip 

 or streak comes to lie temporarily ventrad and anterior to the 

 anterior lip. 



10. This depressed portion of the posterior lip separates in the 

 median or axial line; each half passes laterad, dorsad, and then 

 mesiad, to fuse again in the axial line of the anterior or dorsal lip. 



11. This inequality in the rapidity of the fusion of the anterior 

 or dorsal lip, and of the reopening of the posterior or ventral lip, 

 causes the neurenteric canal for a time to assume an oblique 

 direction. 



