rand: nervous system of LUMBPJCIDyE. 133 



According to this interpretation, the centrosome would lie within the 

 nuclear membrane. 



When the condition of Figures 37 and 38 is reached, it becomes evi- 

 dent that the lightly stained polar region is not included within the nuclear 

 membrane. 



Figure 38 shows a group of cells from the anterior end of a regen- 

 erating cord. At the centre of the group is a large nucleus slightly 

 irregular in form. It contains a single nucleolus and is denser in chro- 

 matin than most resting nuclei. On one side of the nucleus is a lightly 

 stained region, appearing crescent-shaped in the section, and sharply 

 outlined against the clear space which surrounds it and the nucleus. 

 At the mid-periphery of the liglit region is a dark granule. A com- 

 parison of Figure 38 with Figures 31-36 leads to the conclusion that 

 the chromatic masses of Figures 31-36 are the daughter nuclei, and the 

 lightly stained polar regions including the centrosome are not contained 

 within the nuclear membrane, but represent cytoplasmic structures. 



Figure 37 shows a cell from a regenerating brain. The nucleus, con- 

 taining a large proportion of chromatin, still exhibits the polar concavity 

 seen in the earlier " chromatic masses." No nucleolus is yet visible. In 

 this case the lightly stained region on the concave side of the nucleus is of 

 much greater volume in proportion to the nucleus than in Figure 38. 

 Near the mid-border of it is a small deeply stained granule surrounded 

 by a slightly clearer space. Some weak radiations proceed from the 

 granule. In Figure 37, then, we have a nucleus, upon the concave or 

 polar side of which is a considerable mass of cytoplasm containing a 

 centrosome and radiations. But what of the clear space surround iiif^ 

 the nucleus and its polar mass of stained cytoplasm ] In all the stages 

 represented in Figures 31-38, this clear space is present. It can be 

 interpreted only as the space originally bounded by the mother-cell 

 membrane, which has now degenerated. In such a case as Figure 37, 

 is the clear space to be regarded as a part of the cell territory belono-ino- 

 to the nucleus which lies within it, or is the entire daughter cell at this 

 stage to be considered as included within the outline which encloses the 

 nucleus and the dense cytoplasmic mass lying on its concave side 1 I 

 hold the latter to be the correct interpretation. In all of Fio-ures 

 31-38, the lightly stained polar region containing the ceiitrosome consti- 

 tutes the fundament of the cytoplasm. This cytoplasmic fundament 

 increases in volume along with the nucleus, occupying more and more 

 of the space originally bounded by the old cell membrane. 



At all stages it must be said that all the living parts, at least, of 



