OBSERVATIONS ON STRUCTURE OF CELLS AND NUCLEI. 129 



i.e. the uniform network with uniform bright dots in its nodes, 

 belongs to the adult condition of the nucleus. But this is not 

 necessarily limited to cells of the adult, for the nucleus of a cell 

 in the embryo passes just as much through a whole developmental 

 cycle as that of a cell in the adult. Cells of the adult, as well 

 as of the embryo, become mother-cells, and their nucleus, as is 

 now well known, undergoes a series of remarkable changes, the 

 last stage of which, i.e. that of ripeness, is the above condition 

 of a uniform network. 



In conformity with this we find in the earliest, as well as latest 

 stages of the embryonal life, vast numbers of nuclei, which contain 

 just as uniform a network as the nuclei of small cells of the 

 adult ', besides these, there are others in which this network is 

 not so well developed. The same may be said of the nuclei in 

 the cells of the adult. In this respect I quite agree with what 

 Balfour says in his paper of the history of the reticulum in the 

 ova, although I am under the impression that the nuclei of the 

 primitive ova, as depicted in fig. 1 of Plate XVII of his paper, 

 of which he says that they contain a uniformly granular matter, 

 may in reality already include a network, the fibrils of which are 

 very short. I shall have occasion later on to refer to the nuclei 

 of the epithelium of seminal tubes of mammals as containing a 

 dense network of very short fibrils or rods ; the appearances 

 presented here are in many respects similar to those of the nuclei 

 of the primitive ova in the above-named fig. 1 in Balfour's 

 paper, but in the case of the nuclei of the seminal epithelium 

 I am able to trace the reticulum very distinctly. 



I shall have several times occasion to return to the question of 

 the nucleolus in the different epithelial and gland-cells which I 

 shall have to describe in this paper, and I will limit myself to say 

 here with regard to the nucleus of the epithelial cells of the in- 

 testine, that in many instances there is no trace of a nucleolus, 

 and that in some instances there are one or two larger particles 

 contained in the reticulum, the significance of which I have 

 explained above. 



The intranuclear and intracellular network are in connection 

 with each other, just as I described it in the case of the epi- 

 thelial cells of the stomach of newt. 



In some nuclei there exists a special arrangement of the intra- 

 nuclear network in the presence of a layer of circular fibrils 

 situated next the membrane, and arranged parallel to the surface 

 of the nucleus. These fibrils being occasionally viewed perpen- 

 dicularly are seen as a row of dots next the membrane of the 

 nucleus. A similar arrangement had been noticed also by 

 Eimer,^ who describes in some nuclei of cells of Salamandra, 



1 Loc. cit., p. 109, 



