46 Primitive Streak and Notochordal Canal in Chelonia. 



12. Later, the posterior lip in its reopening more nearly keeps 

 pace with the fusion of the anterior lip, and thus the neurenteric 

 canal comes to assume a more nearly perpendicular position. 



13. This process of posterior separation and anterior refusion 

 of the lips is accompanied by the disintegration of that portion of 

 the entoderm which corresponds to the floor of the notochordal 

 canal. 



14. The existence of such a potential canal in the streak region 

 can be inferred from the presence of a primitive groove in the 

 streak, from evidence of degeneration of the lower lying entoderm 

 of this region, and, in rare instances, from the existence of this 

 lower layer, or portions of it, as a distinct layer. 



