334 THOS, H. MONTGOMERY, 



the equator of the cell (Fig. 202); this process shows that they may 

 be drawn into the substance of the cell body, or enter into the con- 

 stitution of the cell membrane, but that they are certainly not retracted 

 into the chromosomes. 



A word as to the cytoplasm during these stages. Near the end 

 of the prophase, when the two pairs of centrosomes are wandering 

 apart, the latter are the centres of strongly marked cytoplasmic asters 

 (Figs. 161—165, Plate 21; Figs. 166-169, Plate 22). A considerable 

 portion of the cytoplasm seems to be included in the formation of 

 these asters, but not all of it, for at their distal ends the astral 

 radiations pass gradually into a reticulum. When the nuclear mem- 

 brane disappears completely these astral radiations have become so 

 reduced, that only few and very delicate pole fibres are to be seen 

 (Figs. 179—182, Plate 22). This is not due to any fault in the 

 fixation process, for side by side in the same section all the various 

 degrees of astral development can be met with. From the stage of 

 the monaster on there is a broad zone in the equator of the cell, 

 where a loose cytoplasmic reticulum is found. On pole views (Figs, 187, 

 188) of the spindle, this zone can be seen very clearly: the loose 

 reticulum is seen to be composed of large, apparently anastomosing 

 fibres, suspended in a structureless fluid, and extending more or less 

 radially from the chromosomes to the cell membrane ; in some cases 

 it appeared that these fibres were actually attached to the chromosomes, 

 but this could not be determined positively. Thus, from the stage of 

 the monaster on, a very large proportion of the cytoplasm seems to 

 continue in a condition very n)uch like that of the rest stage, though 

 less dense, unattracted by the centrosomes, and this in cells where 

 the achromatic spindle extends through the greater length of the cell. 



Apparently the centrosomes attain their greatest dimensions and 

 stain most deeply, just before the disappearance of the nuclear mem- 

 brane , at the time when the astral radiations are most strongly de- 

 veloped ; and from this stage on the centrosomes appear to diminish in 

 size and staining intensity. Certainly it is just at the end of the 

 prophase that they are most distinct, and 1 do not think it due to 

 an illusion that they seem smaller afterwards. The coincidence is 

 interesting, that when the centrosomes are largest and stain most 

 deeply the astral radiations are most fully developed; or in other 

 words, it would seem that when the centrosomes are largest and 

 stain most strongly they exert the greatest atractive influence upon 

 the other cell structures. 



