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W. M. BALDWIN. 



left. Both portions of the embryo are connected with each 

 other by a narrow strip of mesenchymal tissue at the bottom 

 of the epidermal cleft. The notochord is to be seen only in the 

 left half of the embryo with the myoblastic tissue to either 

 side of it, the enteron ventral and the neural tube dorsal. The 

 stage is so early that most of the yolk cells are in an undiffer- 

 entiated condition. 



Figs. 9, 10 and n are sections of one and the same embryo. 



FIG. 9. 



In this the bend of the trunk occurred at about the level of 

 its middle segment. The section-knife encountered both the 

 neural tube and the notochord at their curvature. The un- 

 diflerentiated yolk-mass of the two limbs of the U are connected 

 by a relatively slender commissure-like mass of yolk cells and of 



FIG. 10. 



mesenchymal tissue. The section of Fig. 10 taken at about the 

 level 8 of Fig. 4 demonstrates on the left the transsected noto- 

 chord with the cephalic end of the definitive spinal cord corsal 

 to it, both imbedded in myoblastic cells not yet well differ- 

 entiated. A section of notochord and of spinal cord with the 



