Plate III. 



Living Eggs of Oynthia partita; First to Fourth Cleavage. 



Figs. 25 and 26- Same egg a* the one shown in figs. 21-24; final stages in the first cleavage. 



Fig. 27. Another egg at the close of the first cleavage ; seen from the posterior pole. 



Fig. 28. End view of egg of same stage as preceding, showing the lateral limits of the yellow cres- 

 cent, the clear protoplasm in the upper hemisphere and the yolk in the lower. The 

 anterior portion of the lower hemisphere is composed of light gray material ; this is the 

 gray crescent and gives rise to chorda and neural plate. 



Fig. 2'.). Four-cell stage, viewed from the animal pole. 



Fig. 30. Similar egg seen from the vegetal pole; the crescent covers about half of the posterior 

 blastomeres. 



Fig. 31. Fight-cell stage: the crescent is limited entirely to the two posterior blastomeres at the vege- 

 tal pole : while under observation the furrow between B 4 ' and b 4-2 shifted from the posi- 

 tion indicated by the faint line to that shown by the heavy line, thus giving rise to the 

 "cross furrow" shown in the next figure. 



Fig. 32. Fight-cell stage, viewed from the right side, showing a small amount of yellow protoplasm 

 around all the nuclei. 



Fig. 33. Same stage viewed from the vegetal pole, showing 1% yolk laden endoderm cells and the 

 crescent. 



Fig. 34. Same stage viewed from the posterior-animal pdreTshowing the clear ectodermal cells and 

 the crescent. 



Fig. 35. Same stage seen from the anterior-vegetal pole; yellow protoplasm around all the nuclei. 



Fig. 36. -Fourth cleavage of the egg seen from the vegetal pole. 



* 



