50 KARYOKINESIS. 



into the cytoplasm during nuclear division ; in Cucullanus and Nephelis this loss 

 of nuclear fluid may amount to as much as two-thirds of the volume of the unal- 

 tered nucleus. Biitschli held that this fluid escaped at the two poles of the nucleus 

 and accumulated in the central areas (asters), from which it radiated into the cell 

 body. Further Biitschli observed that the more a daughter nucleus grows, the 

 more the central area of the neighboring radial system diminishes, whence he 

 inferred that the latter furnishes material for the growth of the former. (See 

 Mark, 'SI, p. 321.) 



In 1892 Biitschli reversed his former view as to aster formation, holding that 

 it is due to a flowing of plasma into the spheres or centrosomes and not from them. 

 He supposed that the centrosomes attracted substances dissolved in the enchylemma 

 as a hygroscopic substance attracts water, and that the diffusion movements thus 

 produced cause the astral radiations. Although Biitschli in his 1892 work, and 

 since in 1898 and 1900, maintains that the astral radiations are due to an attraction 

 exerted by the centrosome, he expressly stated in the first mentioned work that it 

 is unimportant whether the diffusion streams move in one direction or the other 

 (z. e., centrifugally or centripetally). 



I fully agree with Biitschli that the astral rays are the expression of diffusion 

 streams. In the process of diffusion the commingling substances may move in 

 opposite directions at the same time, and it is quite possible that the balance of flow 

 between the centripetal and the centrifugal diffusion movements may lead to a cen- 

 trifugal flow at one time and to a centripetal flow at another. 



Bhumbler ('96, '99) has also developed an elaborate theory of aster and spindle 

 formation which is based in the main upon this view of Biitschli's. He holds that 

 the astral rays are reducible to tension on the alveolar radii ; this tension being due 

 to the fact that the centrosomes, and later the nucleus, take up fluids from the sur- 

 rounding plasm. He also holds that the two spheres exert a pull on the nucleus 

 which leads to the formation of the spindle and to the escape of nuclear sap into 

 the equatorial plane of the cell, where the division wall will form. 



I accept Rhumbler's views as to the flow of cell and nuclear substances toward 

 the centrosome, but cannot agree with him that the nuclear sap escapes largely or 

 entirely in the equatorial plane. Much of the nuclear sap as well as the oxychro- 

 matin and linin escapes at the poles of the nucleus and, although nuclear contents 

 escape into the cytoplasm in all directions when the nuclear membrane is com- 

 pletely dissolved, there is no evidence in the cases which I have studied that this 

 has to do with the formation of the division wall. 



Fischer ('99) holds that the spheres of animal eggs are to be explained as 

 substances escaped from the nucleus, and he suggests that the astral rays may be 

 normally formed by the diffusion of substances from the nucleus into the cytoplasm 

 and the production there of non-soluble substances. He considers that such radi- 

 ations are not persistent structures, but that they may appear and disappear re- 

 peatedly during the course of a single division. I agree with Fischer that there is 

 an escape of nuclear substance at the poles of the nuclei, and that the astral rays 



