270 



GENERAL EMBRYOLOGY 



E 



FIG. 124. The development of one of the blastomeres of the two-cell stage of 

 the Tunicate, Cynthia. From Conklin. The yellow material (see Figs. 91, 92) 

 is stippled; the boundary between clear protoplasm and yolk is indicated by a 

 crenated line. 



A. Right half of eight-cell stage; posterior view. J5. Right half of thirty-cell 

 stage; dorsal view. C. Right half of forty-eight-cell stage; dorsal view. D. 

 Right half of sixty-four- to seventy-six-cell stage; dorsal view. E. Right half 

 of gastrula of about 220 cells derived from four-cell stage. The neural plate, 

 chorda, and mesoderm cells, are present only on the right side, and in their 

 normal positions and numbers. F. Right half of young tadpole; dorsal view. 

 Derived from four-cell stage. The notochord consists of a small number of cells 

 which are interdigitating ; muscle-cells and mesenchyme lie on the right side of 

 the chorda, but not on the left side, though the muscle cells have begun to grow 

 around to the left side. The neural plate is normal in position but not in form. 

 m'ch., mesenchyme; ms, muscle cells. 



The cell nomenclature in this and the following figure, differs from that de- 

 scribed in Chapter VI. The right and left halves of the embryo are designated 



