48 SYDNEY J. HICKSON. 



been washed away, shows that these islands are connected 

 together by a very coarse mesh-work of fine protoplasmic 

 strands. 



In a later stage the islands are seen to be more numerous, 

 and the protoplasmic mesh-work somewhat finer. A complete 

 nucleus may be seen in some of these islands, but in others all 

 that can be made out are a few deeply staining granules 

 (figs. 10 and 12). 



In a later stage the nuclei have increased in number in the 

 midst of the yolk, and a few make their appearance in the 

 protoplasmic sheath that surrounds the ovum. 



In these last three stages I have described a process which 

 can only be compared with the so-called free nuclear forma- 

 tion in early insect embryos. Nuclei make their appearance 

 in places which were previously apparently devoid of any 

 nucleus or nuclear structure. Moreover nuclei of various 

 sizes and shapes may be seen in the embryo at the same time. 



It is not reasonable, however, to assume on the insufiScient 

 evidence before us that "free nuclear formation" does actually 

 occur. It seems to me to be much more probable that minute 

 fragments of nuclear substance scattered through the proto- 

 plasmic mesh-work collect together in places, and form by 

 their fusion true recognisable nuclei. In other words, the pro- 

 cess we have under observation is rather one of "nuclear re- 

 generation" than one of "free nuclear formation." 



I have often noticed in ova of these stages an aggregation 

 of the yolk into spherical, polygonal, or irregular lumps, sug- 

 gesting that the egg has undergone some form of complete 

 segmentation (fig. 13). This is not a true process of seg- 

 mentation, however, since the distribution of the nuclei in the 

 spaces between the aggregations and not in their centres shows 

 that it afi'ects the yolk only. It is remarkably similar in 

 appearance to the so-called yolk segmentation of Arthropods, 

 the appearance of the embryo at this stage being very much 

 like that of such a form as Peripatus novse-zealandise, as 

 described by Miss Sheldon (63). This segmentation of the yolk 

 seems to be only temporary, for in embryos in which the 



