8TRUCTUEE OF THE SEGMENTATION NUCLEI. 29 



which differ from one another suflBciently to merit a special 

 description ; three of these were found before the beginning 

 of segmentation, and one in an ovum of two segments. 



a. A spherical structure (diameter, 004! mm.) bounded by 

 a membrane, which is slightly indented at one point, where it 

 sends in a prolongation of itself, which passes through the 

 nucleus to become continuous with the membrane of the 

 opposite side (PI. Ill, fig. 8 a). The prolongation of the 

 membrane across the nucleus is also connected with the mem- 

 brane at another point (on the lower side of the figure), and, 

 in addition, sends off processes which ramify in the substance 

 of the nucleus. The nucleus is made up of a fine spongework 

 of very pale fibrils, which are continuous with the 

 nuclear membrane and with the septum and its pro- 

 cesses just mentioned. In this spongework are a number 

 of deeply-staining more or less spherical bodies. 



The membrane, septum, and its processes stain about as 

 deeply as the strands of the extra-nuclear reticulum, and 

 they appear to be continuous with the fine, pale, 

 little - staining strands, which constitute the main 

 mass of the nuclear spongework. The pale spongework 

 further possesses, as I have already said, a number of bodies — 

 some elongated and branched, others globular — which are, I 

 think, stained rather more deeply than the membrane and its 

 offshoots, and which are likewise continued into the strands 

 of the pale nuclear network. This latter fact is quite easy 

 to see in tlie elongated branched staining fibrils, and the 

 deeply-staining globular bodies, when carefully examined with 

 a high power, present in many cases an angular appearance^ 

 the angles being continued into the pale reticulum. 



As already stated, the nuclear membrane and septum appear 

 precisely similar in structure to the strands of the external 

 protoplasmic reticulum, and the latter are continued 

 directly into the former. The pale nuclear reticulum is 

 also similar to the extra-nuclear reticulum, diflfering only in 

 intensity of staining. 



It is also directly continued into the nuclear membrane and 



