4o6 Ralph S. Lillie 



considerations, is in striking agreement with the view propounded 

 by Conkhn-'' some years ago in his studies of karyokinesis in the 

 Crepidula egg. Some of his conclusions on the physiology of this 

 process should be quoted. "The nuclear membrane appears to 

 permit the passage of materials inward but not outward during the 

 resting period; whereas the escape of nuclear material into the cell 

 is brought about by the disappearance of the nuclear membrane 

 during karyokinesis." In Crepidula there can be demonstrated 

 cytologically "a very extensive interchange of material between 

 the nucleus and the cytoplasm;" "a large part of that most 

 characteristic nuclear substance, the chromatin, passes into the 

 cytoplasm in the form of oxychromatin during every cell-cycle, 

 while a relatively small part is reserved for the purpose of repro- 

 ducing the daughter-nuclei." This passage of nuclear material 

 (presumably nucleo-proteid in nature) into the cytoplasm is re- 

 garded as a fundamentally important condition of the subsequent 

 changes undergone by the latter. These phenomena appear to be 

 characteristic of mitosis in general and essentially similar conditions 

 have been described for a number of cells. In the starfish egg by far 

 the greater part of the chromatin is set free in the cytoplasm during 

 the first maturation division." In Chaetopterus also the greater 

 part of the germinal vesicle consists of a "residual substance" 

 which is set free in the cytoplasm at the first maturation-division 

 and plays an important part in the future development.^^ It is 

 natural, in view of the probable nucleo-proteid nature of at least 

 certain enzymes, to regard the above "oxychromatin" or "residual 

 material" as consisting — at least in part — of the ferments con- 

 cerned in the chemical processes — largely oxidative in their nature 

 as shown clearly by the conditions in the starfish-egg — that deter- 

 mine the later characteristic changes in the cytoplasm. The 

 ascertained cytological facts are thus in essential harmony with 

 the above hypothesis. 



Whether the change in the cytoplasm depends primarily on 

 increased oxidations or on other conditions is scarcely decided as 



^ Journal of the Academy of Natural Sciences of Philadelphia, second series, vol. xii, pt. I, 1902. 



-' Wilson and Mathews: Journal of Morphology, vol. x, p. 334, 1895. 



^* Cf. F. R. Lillie; Journal of Experimental Zoology, vol. iii, p. 153, 1906. 



