134 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the daughter cell are included within the limits of the nucleus and its 

 polar cytoplasmic fundament. It may be that the surrounding clear 

 space contains fluid material derived from the degenerated parts of the 

 mother cell, and that the growing cytoplasm of the daughter cell 

 utilizes some of this material. In that sense only can the clear space 

 be regarded as actually a part of the young cell. 



Figure 39 shows two cells from a regenerating suboesophageal gan- 

 glion. The nucleus at the left is in a typical resting condition, having 

 a chromatic network and large nucleolus. Its cytoplasm is massed at 

 one end of it and contains the centrosome surrounded by a dark ring. 

 The nucleus at the right shows no nucleolus. The cytoplasm is massed 

 at one end of the nucleus and contains a clear space at the centre of 

 which is a dark granule with some weak radiations. The young cells 

 of Figures 34 and 35 may readily be imagined to become such cells as 

 are seen in Figure 39. 



Figures 40 and 41 represent cells from the brain after five weeks' 

 regeneration. The nuclei have the form and structure typical for those 

 of nei've cells. The cytoplasm in both cases is collected upon one side 

 of the nucleus and contains an unmistakable centrosome and radiations, 

 constituting a centred system like that which has been described in 

 nerve cells of the normal worm. No nerve processes from these cells 

 could be seen. Cells like these may be derived from cells like those in 

 Figures 37 and 39 simply by the increase in volume of nucleus and 

 cytoplasm. By this growth the space originally bounded by the old 

 cell membrane becomes entirely filled, and there is no longer a clear 

 space about the growing cell. 



In Figure 36 the large nucleus at the extreme left possesses a consid- 

 erable cytoplasmic mass, which contains evidence of a centred system, 

 although no distinct centrosome could be seen. The nucleus is peculiar 

 in lacking a nucleolus. The cell at the extreme right has a pear-shaped 

 form, and there is some evidence of a process at the smaller end. On 

 the side of the nucleus toward the larger end of the cell is a region of 

 denser cytoplasm with a lighter centre, but no centrosome or radiations 



can be seen. 



Figure 42 shows a group of three cells from a suboesophageal gan- 

 glion of thirty-four days' regeneration. The three nuclei lie at differ- 

 ent levels, the smallest one being lowest. A centrosome and radiations 

 may be seen close to each of the two larger nuclei, and on the side 

 toward the greatest cytoplasmic mass. 



