KARYOKINESIS. 51 



represent diifusion streams through the cell body, but I am not sure that I under- 

 stand him when he says that the rays arQ composed of non-soluble substance, since 

 they certainly disappear (as he also maintains) either by dissolving in the cyto- 

 plasm or by being absorbed into the sphere. 



Meves ('99) criticises Fischer's views on aster formation by saying that such 

 rays as Fischer describes could not grow interstitially, as normal raj's and spindle 

 fibres are known to do ; sometimes also extensive rays appear in the anaphase, 

 long after the mingling of nuclear and cytoplasmic substances. If, however, these 

 rays be considered as diffusion streams to or from the centrosome. in the sense of 

 Biitschli, these criticisms lose most, if not all, of their force. Finally, that the 

 astral rays are not fixed structures stretching between the centrosome and the cell 

 membrane, as Heidenhain and Kostanecki hold, is shown by the fact that in many 

 mitoses the spindle is free to turn and move through the cell, and yet the astral 

 raj's show neither twisting, bending, nor distortion. This is shown especially well 

 in the first maturation, and in the first three cleavages of Crepidula^ where there 

 are considerable movements of the amphiaster even after the metaphase ; but in no 

 case is there a corresponding bending of the rays, as there would be if these were 

 fixed structures (see observations of Ziegler, Lillie, et al., Part II, Sec. III). 



(d). Chromatic Elimination. — In the maturation and early cleavages of the 

 eggs which I have studied, the total amount of chromatin which is transformed into 

 linin or dissolves and escapes into the cell body is greater than that which goes to 

 form the chromosomes; the amount of cytoplasm in the cell is also noticibly greater 

 after the nuclear membrane is dissolved than before. 



In this connection other observations of a somewhat similar character maj^ be 

 recalled. Almost all persons who have studied the maturation of the egg, have 

 commented upon the large quantity of nuclear material which is set free into the 

 cell body during the fii'st maturation division. In the starfish, according to Wilson 

 ('95, p. 458), at least nine-tenths of the chromatin is thus set free. Gardiner ('98, 

 p. 97) estimates that in the egg of Polychcsrus not more than one five-hundreth 

 part of the chromatin which is present in the germinal vesicle goes into the chro- 

 mosomes, all the rest being thrown out into the cell. Most observers agree in 

 identifying as chromatin this nuclear material which escapes into the cell body, 

 though in most cases it stains less deeply than the chromosomes and its subsequent 

 dissolving shows that it must be different from the chromosomes, which never dis- 

 solve. Gardiner ('98, p. 98) argues that there must be two kinds of chromatin, the 

 one soluble, the other not, and Griffin ('99) believes that the soluble chromatin arises 

 as a nuclear reticulum which at first takes plasma stains and later nuclear ones. 



Boveri's ('92 and '99) observations on the diminution of the chromosomes in 

 the somatic cells ol A scar is may be recalled in this connection. In this case the 

 ends of the chromosomes pass into the cytoplasm during the mitosis and there 

 gradually undergo solution or disintegration. This case, however, differs greatly 

 from that of Crepidula since it occurs only in differentiation of somatic cells, 

 whereas in Crepidula the outflow of nuclear material occurs at each and every 



