30 SEGMENTATION AND FORMATION OP THE LAYERS. 



septum. The apparently isolated, deeply-staining bodies, both 

 globular and branched, are also, as I have said, continuous 

 with the pale reticulum ; so that this nucleus may be described 

 as consisting of a portion of the spongework of which the 

 ovum is composed, the nuclear protoplasm differing only from 

 the external protoplasm in the fact that the staining matter is 

 aggregated into special parts of the spongework instead of 

 being uniformly diffused throughout the latter as in the 

 extra-nuclear protoplasm. The apparent nuclear membrane is 

 simply part of the protoplasm at the junction of the modified 

 (nuclear) and unmodified (cell- substance) part of the proto- 

 plasmic network. 



The question now presents itself j why do parts of the 

 nuclear spongework appear more deeply stained than the rest ? 

 Either the parts thus staining are of greater mass than the 

 rest, extending through the whole thickness of the section, 

 while the pale strands are so fine that several of them, separated 

 by the spaces of the meshwork, lie above one another in one 

 transverse section ; or there is a special chromatic substance, 

 distributed at intervals in the intra-nuclear spongework. If 

 the former is the correct answer the difference in colour 

 between the pale and stained parts of the network is of the 

 same nature as the difference in the colour of blood or any 

 other coloured fluid when viewed in a thick or in a thin 

 layer. 



Though there may be something in this way of looking at 

 the deeply staining parts of the nuclear spongework, I do not 

 think that it entirely explains the matter. 



It may here be mentioned that the meshes of the extra- 

 nuclear reticulum immediately around the nucleus are much 

 smaller than in parts remote from the nucleus, so that in a 

 transverse section several strands will lie one above the other 

 in even the thinnest section, while away from the nucleus, 

 where the meshes are coarser, a smaller number of strands will 

 coincide. Hence the protoplasm immediately around the 

 nucleus appear more deeply stained than do the peripheral 

 portions. 



