DEVELOPMENT OE DISTIOHOPOEA VIOLACEA. 69 



mediate in character between fragmentation and bipolar 

 karyokinesis seems to be probable from the discovery of 

 pluripolar mitosis in the inflamed cornea by Schottlaender 

 (50), and other atypical nuclear divisions in the spleen of the 

 white mouse by Arnold (1), &c. 



We have, then, a series of phenomena in the division of 

 nuclei, with typical karyokinesis at one end and direct frag- 

 mentation at the other. The occurrence of any one kind or 

 the other is, in my opinion, determined by the forces which act 

 simultaneously upon nucleus and cell plasm. If these forces 

 are of such a kind as to drag the cell plasm into two equal 

 halves, the nucleus is also dragged into two equal halves with 

 mitosis ; if, on the other hand, the forces are irregular and act 

 from many centres at the same time, the nucleus fragments 

 irregularly. 



These views seem to me to be supported by the statement of 

 Flemming (11) quoted by Sedgwick, that " the first change 

 observable in a cell whose nucleus is about to divide is in the 

 extra-nuclear protoplasm," and by Burger's (7) recent con- 

 clusions concerning the meaning of the spheres of attraction. 



List of References. 



1. Arnold, J. — " Weitere Mittheilungen iiber Kern- und Zelltheilung in 



der Milz," ' Archiv f. mikr. Anat.,' xxxi, p. 541. 



2. Beltzow, a. — " Zur Kegeneration des Epithels der Harnblase," ' Vir- 



chow's Archiv,' 97, 1884.. 



3. Blochmann, p. — " Ueber die Richtungskorper bei Insecteneiern," 



' Morph. Jb.,' xii, 1887. 



4. Brandt, K. — " Die Koloniebildenden Radiolarien," ' Fauna und Flora 



des Golfes von Neapel,' xiii, 1885. 



5. Brauer, a. — " Ueber die Entwicklung von Hydra," ' Z. wiss. Zool.,' 



Hi, Hft. 2, 1891. 



5a. Brauer, A. — "Ueber die Entstehung der Geschlectsprodukte und 

 die Entwicklung von Tub ularia mesembryanthemum," 'Z.wiss. 

 Zool.,' lii, Hft. 4, 1891. 



6. Brooks, W. K., and Herrick, F. H. — " Tiie Embryology and Meta- 



morphosis of the Macroura," ' U.S. National Acad, of Sciences,' vol. 

 V, Fourth Memoir. 

 VOL. VI. 7 



