124 RICHARD ASSHETON. 



large primary segment (fig. 3jZ..), and smaller ones derived 

 from the small primary segment (v. fig. 3j S.). If, then, we rely 

 upon the only character at present possible, that is to say, 

 upon the size of the segment, we are bound to conclude that 

 not only does the process of segmentation proceed with great 

 irregularity, but that also there is no evidence of the descend- 

 ants of the larger primary segment ever forming a cap and 

 subsequently enveloping the descendants of the smaller primary 

 segment. 



I believe, rather, that descendant segments of the larger 

 primary segment become intermingled quite irregularly with 

 the descendants of the smaller primary segment, for this un- 

 doubtedly affords a better explanation of the appearance of 

 embryos like that shown in fig. 12 or fig. 15. 



Fig. 11 is an outline drawing of a specimen taken from a 

 rabbit which was killed at the completion of the 39th 

 hour. In this animal seven of the eight embryos found were 

 in the eight-segment stage. It is extremely difficult to mea- 

 sure the segments with sufficient accuracy to be of any service, 

 and although I measured them I shall not give the results. In 

 this case, as shown by the fig. 11, there was very little dif- 

 ference in size, and none, so far as I could judge, in texture. 

 There was one curious feature which is worth mentioning, but 

 I do not attach any importance to it. The larger polar body 

 was visible between the embryo and the zona radiata. The 

 smaller of the two was inside, or rather mingled with the seg- 

 ments of the eral}ryo. It is quite possible that this frequently 

 occurs, for the polar bodies seem very often to disappear en- 

 tirely. It would be of interest to determine whether, when 

 this is the case, the polar bodies, ever under the altered con- 

 ditions, acquire a renewed activity and give rise to segments 

 whose descendants become part of the embryo. 



I have as yet no evidence as to which sphere commences the 

 next series of cell division. 



At about the 47th hour the embryo has the typical morula 

 form, and is made up of a number of segments (sixteen to 

 twenty), which very frequently present great diversity in size. 



