128 



J. Thomas Patterson. 



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16 17 



Fig. 14. — A diagram of a seven-celled stage, showing the distribution of 

 the cleavage and supernumerary sperm nuclei. The egg was taken from the 

 isthmus about three and three-fourths hours after the estimated time of 

 fertilization. A— B, plane of the section shown in Fig. IS, and C — D that 

 of Fig. 19. X 18. 



Fig. 15.— An interesting blastodisc showing a large number of marginal 

 cells in the process of formation. The egg was taken from the isthmus. X 18. 



Fig. 16.— a blastodics showing a comparatively regular form of cleavage in 

 the eight-celled stage. The egg was taken from the isthmus about four hours 

 after fertilization. The letters indicate the cells that are probably homolo- 

 gous ; and the numbers, the first and second cleavage planes. Three acces- 

 sory cleavage furrows are shown. X 18. 



Fig. 17. — An early stage showing an eccentric cleavage, with the displace- 

 ment toward the anterior, g.a.c, a group of five small accessory cleavage 

 cells. The egg was taken just as it was passing into the shell-gland. 



