136 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



times appear to couuect certain larger granules on two different primary 

 radiations. This cell is one of the first type, lacking anything that 

 could be called a "sphere." 



V, General Conclusions. 

 1. Mitosis in the JSTervous Fundaments. 



To summarize briefly the process of mitosis as seen in the cells of the 

 ganglionic fundaments : 



The prophase is accompanied by a turgescence of the cell ; a dis- 

 tinct cell membrane is formed ; the nuclear membrane disappears ; 

 the chromatin takes the form of nearly spherical chromosomes ; the 

 region between the chromosomes and the cell membrane is nearly or 

 quite clear; a spindle appears with its centrosomes very minute, if 

 visible at all. 



In the metaphase a distinct cell membrane is still present; the 

 spindle with its equatorial plate of chromosomes lies sharply outlined 

 in the cell body, wliich is otherwise nearly or quite free from any solid 

 material ; generally the centrosomes are clearly to be seen at the spindle 

 poles and often they become fairly conspicuous objects. 



In the later phases the chromosomes separate and move toward the 

 poles, each daughter group fusing into a compact mass, which is concave 

 on its polar side ; the centrosome remains visible at the apex of the old 

 spindle, the end of which forms a lightly staining region between the 

 centrosome and the concave surface of the chromatic mass ; the inter- 

 zonal filaments occupy a barrel-shaped region; an equatorial constriction 

 of the cell membrane appears. The ingrowth or differentiation of an 

 equatorial membrane between the two daughter cells follows, accom- 

 panied by the constriction of the barrel-shaped figure to the form of 

 two cones with apices together at the plane of the equatorial membrane. 

 As a result of this decrease in the volume of the figure, some of the sub- 

 stance of the barrel-shaped figure, including a few of its filaments, is 

 left outside the limits of the constricted figure. This substance disap- 

 pears later. 



During the forming of the equatorial membrane, the old cell 

 membrane (now become the daughter-cell membranes) undergoes 

 degeneration, and finally the new equatorial membnino also disappears. 

 At this period, then, the constricted figure lies sharply outlined in an 

 irregular clear space wliich is not definitely outlined, not enclosed in a 



