52 KARYOKINESIS. 



mitosis. Hacker ('97) has described an elimination of nuclear constituents in the 

 Keimbahn of Cyclops; in the first cleavage a large number of granules ("ekto- 

 somes"), which Hacker considers escaped nucleoli, collect around one attraction 

 sphere but not around the other. This process is repeated in subsequent cleavages, 

 the cells in which the ektosomes appear marking out the Keimbahn. Finally, in 

 the division of the genital cells the ektosomes are found around the entire spindle 

 figure. The elimination of the ektosomes in Cyclops, like the diminution of the 

 chromosomes in Ascaris, differs fundamentally from the chromatic elimination in 

 Crepidula, in that the latter occurs in all the cleavages irrespective of whether the 

 blastomeres are progenitors of the germ cells or not. 



In the ovarian eggs of many animals an elimination of nuclear constituents 

 has been observed (for a list of these cases see Meves, '94, p. 149); all these cases 

 deal with elimination during the resting period of the nucleus. On the other hand 

 my observations mentioned above, as well as those of Wilson ('96, p. 141) on Nereis, 

 Mathews ('95) on Asterias, Gardiner ('98) on PolychcBrus, Griffin ('99) on Thalas- 

 sema, and many others, show that there is an escape of chromatic substance from 

 the nucleus into the cytoplasm during the period of mitosis. In the cases just 

 mentioned this elimination occurs during the first maturation division, and Griffin 

 at least, affirms that it does not occur in the cleavage mitosis. In Crepidula, on 

 the other hand, it occurs in every mitosis (except that of the second maturation), 

 though it is, of course, most evident where the nucleus is large and the amount of 

 chromatin great. 



In this connection the theoretical conclusions of De Vries, Weismann and Roux, 

 concerning the nuclear control of the cell should be recalled. De Vries holds that 

 there is an actual migration of pangenes from the nucleus into the. cell body, these 

 pangenes giving character and direction to all cytoplasmic processes, in fact, both 

 De Vries and Weismann assume that the entire cytoplasm is the product of the 

 pangenes. Roux holds that the nuclei become progressively specialized during 

 development, and that these specialized nuclei determine the character of the cyto- 

 plasm, but he does not suggest how this determination occurs. Weismann accepts 

 and unites both the views of De Vries and those of Roux. 



Judging these theories by the facts of chromatic elimination in Crepidula and 

 other gasteropods, I am compelled to conclude that in all nuclei the chromatin 

 appears the same in character, differing only in quantity ; in all nuclei the chro- 

 matin is differentiated into oxychromatin and basichromatin, the latter alone form- 

 ing the chromosomes, wliile the former is eliminated ; there is no evidence of 

 progressive differentiation of the nuclei. That these facts, however, are not con- 

 clusive against the theory of Roux is shown by the fact that in Ascaris there is a 

 specialization of the somatic cells as distinguished from the germ cells ; if such a 

 specialization occurs in Crepidula it must begin at a much later period than in 

 Ascaris. On the other hand, the fact that the eliminated chromatin is differentially 

 distributed to the cleavage cells (see Part II, Sec. II) may be held to afford evidence 

 of the fact that it plays some part in the differentiation of blastomeres. 



