342 



REPRODUCTION 



development consist in the formation of the neural canal, chorda 

 dorsalis, or notochord, and mesoblastic somites. 



Neural Canal. About the fourteenth day, along underneath 



the primitive groove, the cells of the ectoderm become thickened 

 to form the medullary plate. The edges of this longitudinal 

 plate soon begin to curl up, and thus form the medullary furrow, 

 or groove. (Fig. 99.) The margins of the adjacent ectoderm 



