138 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



of outside material and its transformation into a dense protoplasm. As 

 already stated, the cytoplasm in the smaller cells is denser, more finely 

 granular and homogeneous than in the larger cells. It seems highly 

 probable that the fluid material resulting from the degeneration of parts 

 of the mother cell is utilized by the growing cytoplasm of the daughter 

 cells, which finally come to occupy the territory originally filled by the 

 mother cell. It is commonly the case that the cytoplasm becomes more 

 or less fluid during the earlier phases of mitosis, having a clear appearance 

 in preparations; especially is this the case immediately about the 

 nucleus or the spindle. But in the usual forms of mitosis, the cyto- 

 plasmic structure reappears throughout the body of each daughter cell 

 during the later phases, and the daughter nucleus, during its reconstitu- 

 tion, lies in a cytoplasmic mass which is obviously half that of the 

 mother cell. The mother cytoplasm undergoes only a temporary 

 alteration in structure. In the mitosis of the cells of the ganglionic fun- 

 daments with which we are dealing, there is, on the contrary, nothing 

 which suggests the reappearance of the old cytoplasmic structure through- 

 out the bodies of the daughter cells, but a growth of new cytoplasm 

 takes place progressively outward from the polar region of the nucleus. 

 The end of the old spindle lying between the centrosome and the daughter 

 chromatic 7nass (nucleus), together with the centrosome, contains the sub- 

 stance which effects the regeneration of the cytoplasm. 



This regeneration of the cytoplasm of newly divided cells takes place 

 only among the cells of the nervous fundaments. It is found in none 

 of the other regenerating tissues. In all of the preparations from which 

 my figures have been taken, mitosis of the ordinary type may be found 

 in other regenerating tissues. In the dividing cells of the cicatrix there 

 is at all phases a more or less dense mass of cytoplasm about the 

 spindle figure. The mother cytoplasm in these cases is divided in the 

 usual way, one half persisting, without degeneration, about each daugh- 

 ter nucleus. In cells of the epidermis, of the alimentary epithelium, 

 and in nuclei lying in the muscle layers, the mitosis is accompanied by 

 no sign of degeneration and subsequent regeneration of the cytoplasm. 

 In cells of the brain sheath itself, or in cells lying immediately outside 

 it, the telophase shows some dense cytoplasm about each daughter 

 nucleus, whereas, in the same preparations, telophases within the brain 

 fundament exhibit the conditions which have been described, — the 

 absence of structure outside the spindle figure itself. Moreover, in the 

 nervous fundaments, at least in their later stages, all of the mitoses are 

 of the type described. No dividing cells whatever were found jjre- 



