152 Edwin G. Conkltn. 



Normal Developmext of Cynthia partita, Gastrula to Tadpole; X 333. 



The neural plate or tube is finely stippled, the chorda coarsely stippled; muscle cells are shaded 

 by vertical lines, mesenchyme by transverse lines. 



Figs. 7 and 8. Ventral and dorsal views of a gastrula (180-cell stage), showing T-shaped blastopore, 

 neural and chorda plates, mesenchyme and muscle cells. Most of the cleavage cells are in the ninth 

 generation. 



Figs. 9 and 10. Two views of the same gastrula from the dorsal pole; Fig. 9, showing the super- 

 ficial cells, Fig. 10, those at a deeper level. The overgrowth of the dorsal lip of the blastopore and the 

 approximation of the muscle cells of each side toward the median plane hav.e reduced the blastopore 

 to a longitudinal groove in the posterior half of the embryo. The ectoderm cells are in the tenth genera- 

 tion and there are in the entire embryo about 360 cells. 



Fig. II. Dorsal view of an embryo in which the neural plate (n. p.) is closing to form the neural 

 tube (n. t.) Beneath the nerve tube is the notochord and on each side of the latter is shown a row of 

 muscle cells (ms.) At the posterior end of the muscle rows is the caudal mesenchyme, at their anterior 

 end the trunk mesenchyme (m'ch.) 



Fig. 12. Young tadpole viewed from the left side, showing three rows of large muscle cells (ms.) 

 along the side of the notochord (ch.); dorsal to the latter is the nerve tube (n. t.); anterior to the muscle 

 rows is the trunk mesenchyme (m'ch.); ventral to them is the ventral or caudal endodem (v. end.") 



