STRUCrUKE AND DEVELOPMENT OF VERTEBRATE OVARY. 437 



both a vitelline membrane and zona radiiita. E. Van Beneden* 

 has, morc^over, shown tkat they are also provided at a certain 

 period with a delicate membrane within the zona. 



The reticulum of the germinal vesicle. — In the course of des- 

 cription of the ovary it has been necessary for me to enter with 

 some detail into the structure of the nucleus, and I have had 

 occasion to figure and describe a reticulum identical with that 

 recently described by so many observers. The very interesting 

 observations of Dr. Klein in the last number of this Journal have 

 induced me to say one or two words in defence of some points in 

 my description of the reticulum. Dr. Klein says, on page 323, 

 "' I have distinctly seen that when nucleoli are present — the 

 instances are fewer than is generally supposed ; they are accu- 

 mulations of the fibrils of the network." I have no doubt that 

 Klein is correct in asserting that nucleoli are fewer than is gene- 

 rally supposed; and that in many of these instances what are 

 Cidled nucleoli are accumulations, " natural or artificial," of the 

 fibrils of the network ; but I cannot accept the universality of the 

 latter statement, which appears to me most certainly not to hold 

 good in the case of ova, m which nucleoli frequently exist in the 

 absence of the network. 



Again, I find that at the point of intersection of two or more 

 fibrils! there is, as a rule, a distinct thickening of the matter of the 

 fibrils, and that many of the dots seen are not merely, as Dr. 

 Klein would maintain, optical sections of fibrils. 



It appears to me probable that both the network and the nucleoli 

 are composed of the same material — what Hertwig calls nuclear 

 substance — and if Dr. Klein merely wishes to assert this identity 

 in the passage above quoted, I am at one with him. 



Although a more or less distinct network is present in 

 most nuclei (I have found it in almost all embryonic nuclei) 

 it is not universally so. In the nuclei of primitive ova I 

 have no doubt that it is absent, though present in the unmodified 

 nuclei of the germinal epithelium ; and it is present only in a 

 very modified form in the nuclei of primitive ova undergoing a 

 transformation into permanent ova. Tlie absence of the reti- 

 culum does not, of course, mean that the substance capable of 

 forming a reticulum is absent, but merely that it does not assume 

 a particular arrangement. 



One of the most interesting points in Klein's paper, as well as 

 in those of Heitzmann and Euner, is the demonstration of a con- 

 nection between the reticulum of the nucleus and fibres in the 

 body of the cell. Such a cotmection [ have not found in ova, 

 but may point out that it appears to exist between the subgerminal 

 nuclei in Elasmobranchs and the protoplasmic network in the yolk 



^ Loc. cit. 



