OF THE VERTEBRATE OVARY. 613 



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. The absence of the reticulum does not, 

 of course, mean that the substance capable of forming a reti- 

 culum 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 Eimer, is the demonstration of a 

 connection between the reticulum of the nucleus and fibres 

 in the body of the cell. Such a connection I have not found 

 in ova, but may point out that it appears to exist between the 

 subgerminal nuclei in Elasmobranchs and the protoplasmic net- 

 work in the yolk in which they lie. This point is called attention 

 to in my Monograph on Elasmobranch Fishes, page 39 1 , where it is 

 stated that " the network in favourable cases may be observed to 

 be in connection with the nuclei just described. Its meshes are 

 finer in the vicinity of the nuclei, and the fibres in some cases 

 appear almost to start from them." The nuclei in the yolk are 

 knobbed bodies divided by a sponge work of septa into a number 

 of areas each with a nucleolar body. 



1 [This Edition, p. 252.] 



