120 



EICHARD ASSHETON. 



and find that the longitudinal and transverse axes of the one 

 measure exactly the same as those of the other. 



A tabular view of the measurements of these two first cleavage 

 segments may be of interest, showing how the size of one 

 specimen may vary with that of another, and the variation in 

 size of the two segments of one and the same specimen. 



Each segment of each specimen when examined immediately 

 after the death of the animal showed a denser, more granular 

 inner portion, and a clearer, almost hyaline outer layer, the 

 nucleus being situated in the denser inner portion (v. fig. 2). 

 This difference is more evident in the early stages of segmen- 

 tation, up to the time that there are twelve to sixteen seg- 

 ments, than later. 



Stage with Four Segments. 



The second plane of cleavage seems to be at right angles to 

 that of the first. It appears that the two segments divide 

 about, if not exactly, at the same time. This occurs about 

 twenty-five or twenty-six hours after coition. The time between 

 the segmentation of one into two and between two into four 

 appears to be nearly two hours. Since there may be some 

 difference in size between the two primary segments, it follows 

 that there is also very frequently a difference in size between 



