No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 529 



he finds that in mitosis it changes into chromatin. Rabl ('85, 

 larval cells of amphibians) and O. Schultze ('87, ova of Raiia 

 and Triton) contend that the nucleolar substance takes some 

 part in the formation of the nuclear filaments ; but Born ('94) 

 subsequently found that these filaments stand in no connection 

 with the nucleolar substance. Holl ('93, ovum of Mus) finds 

 that the central granules of the nucleoli wander out of them 

 and so become the chromosomes. Van Beneden ('75, ovum of 

 Lepus) originally supposed that the nucleolus becomes the first 

 pole body. Kastschenko ('90, ova of Selachii) finds that all the 

 nucleoli disappear in the spirem stage, while Rijckert ('92) 

 finds that a few of them pass into the cytoplasm. Stuhlmann 

 ('86, ova of Insecta) finds that the nucleoli gradually disappear 

 during the maturation of the egg ; and similar conclusions 

 were reached by Stauffacher ("93, Cyclas), Rhumbler ('95, 

 Cyphoderia), Sheldon ('90, Pcripatus), Heathcote ('86, Juliis), 

 Van der Stricht ('95, Amphioxus), Braucr ('92, Brancliipus), and 

 Vejdovsky ('82, Sternaspis). Auerbach ('96, spermatogonium 

 of Paliidina) holds that the nucleolar substance becomes incor- 

 porated with the chromatin elements. Meunier ('86) and Moll 

 ('93) for Spirogyra, and Carnoy ('85) for other cells also, hold 

 that the chromosomes are derivatives of the chromatin skein of 

 the nucleolus. Heuser ('84, mitoses of various plant cells) con- 

 tends that the nucleoli become gradually apposed to the nuclear 

 filaments, and that their substance unites with these elements, 

 though in some cases a superfluous portion of the nucleolar sub- 

 stance may be discharged from the nucleus. Korschelt ('95, 

 ovum of OpJiryotrocha) finds that the nucleolus gradually dis- 

 appears by dissolving in the nuclear sap, and believes that a part 

 of this substance may be introduced into the nuclear filaments. 

 Zacharias ('85) somewhat prematurely concludes that the nucleoli 

 always disappear in mitosis. Tangl ('82) finds that in Hetiierocal- 

 lis, in uninucleolar nuclei, the nucleolus dissolves in the nucleus, 

 but in those which are multinucleolar one may pass out into the 

 cytoplasm ; in Hespents and Cismm they gradually disappear. 

 Humphrey ('94, plant cells) holds that "die Nucleolen in einigen 

 Fallen aus der Kernhohle, bevor sie von den karyokinetischen 

 Kraften angegriffen werden, austreten konnen." 



