eand: nervous system of lumbeicid^. 137 



membrane, and not divided by an equatorial membrane (Fig. 30). 

 The interzonal filaments degenerate, leaving the two daughter chromatic 

 masses and their accompanying polar structures lying in a common 

 clear space (Fig. 33, « and /5). The chromatic mass is the nucleus ; the 

 lightly stained conical polar region with the centrosome at its apex is 

 the fundament of the cytoplasm. 



The chromatic mass, enclosed within its new nuclear membrane, 

 breaks up into granules, which become the chromatic parts of the 

 resting nuclear network. The polar concavity persists during the earlier 

 growth of the nucleus. 



Tlie polar cytoplasmic fundament increases in volume along with the 

 nucleus, the centrosome persisting through all the growth of the cyto- 

 plasm, and becoming the centre of the radiating system of the resting 

 cell. 



That the spherical membrane seen in the prophase (Fig. 21) is a 

 cell membrane and not an expanded nuclear membrane admits of no 

 doubt when its fate is considered. It is identical with the membrane 

 which encloses the clear space surrounding the figure in the metaphase 

 (Figs. 22-24), and it is this membrane which constricts during the 

 later phases, in connection with the formation of the equatorial mem- 

 brane. Moreover, the centrosome in the daughter cell lies outside the 

 nucleus. During the prophase, therefore, we should not expect to find 

 it within the nuclear membrane. 



The peculiar feature in the reconstitution of the daughter cells is the 

 complete degeneration, during the telophase, of all parts of the mother 

 cell outside the limits of the spindle figure, together with the newly 

 formed equatorial membrane. Still later, the interzonal filaments 

 having disappeared, there comes a period when all the living parts of 

 each daughter cell consist of the compact chromatic mass (nucleus) 

 and its polar region (cytoplasmic fundament), including the centrosome. 



2. Development op the Nerve Cells. 



In the pi'ogress of the nucleus toward the resting condition there is 

 little, if any, increase in the volume of the chromatin. The growth of 

 the nucleus is due to the increase in its fluid contents. As nearly as 

 can be judged, the total volume of the scant chromatin in the large 

 resting nucleus is about the same as the volume of the compact chro- 

 matic mass immediately after mitosis. 



The growth of the cytoplasmic fundament involves the assimilation 



