OTHER MODES OF NUCLEAR DIVISION 213 



tain shall be properly distributed to the reproductive cells; and also in 

 developing tissues and organs, so that differentiation may proceed nor- 

 mally. On the other hand, several workers (Meves; Flemming in his 

 later papers) admit that amitosis may not affect any hereditary powers 

 which the nuclei concerned may possess. Child (1907, 1911), who re- 

 ports amitosis in both the somatic and germ cells of certain animals, 

 where it appears to play an important role in the developmental cycle, 

 strongly urges that such facts render the hypothesis of chromosome in- 

 dividuality highly improbable, and that our conceptions of the r61e of 

 the cell organs in heredity must be greatly altered. 



The hopelessly unsettled state of opinion on this question may be 

 illustrated by the list of authors and their views cited by Conklin (1917). 

 That amitosis frequently occurs in the process of normal cell differ- 

 entiation, and therefore constitutes evidence against the chromosome 

 theory, has been held by Nathansohn (1900), Wasielewski (1902, 1903), 

 Gurwitsch (1905), Hargitt (1904, 1911), Child (1907, 1911), Patterson 

 (1908), Glaser (1908), Jordan (1908), Jorgensen (1908), Maximow (1908), 

 Moroff (1909), Knoche (1910), Nowikoff (1910), and Foot and Strobell 

 (1911). Several of these investigators, together with R. Hertwig (1898), 

 Lang (1901), Calkins (1901), Herbst (1909), Godlewski (1909), and 

 Konopacki (1911), see no principal distinction between amitosis and 

 mitosis, believing that both may occur without interfering with normal 

 differentiation. 



Haecker (1900), Nemec (1903), and Schiller (1909) dissented from the 

 above view, which was also strongly contested by Boveri (1907) and 

 Strasburger (1908). Richards (1909," 1911) and Harman (1913) failed to 

 confirm the results of Child on amitosis in cestodes, but Child (1911) 

 reasserted his view, which was supported by Young (1913). Schurhoff 

 (1919), working on Podocarpus, emphatically states that a nucleus which 

 has once undergone true amitosis is incapable of dividing mitotically. 

 Sakamura (1920) is of the same opinion. 



In a careful study of maturation and cleavage in Crepidula plana 

 Conklin (1917) finds that the nuclei divide only by mitosis. There are 

 many apparent cases of amitosis, but upon careful examination they all 

 prove to be only various modifications of the regular mitotic process. 

 Such modifications are these : the scattering of the chromosomes and their 

 failure to unite into a single nucleus; mitosis without cytokinesis, giving 

 cells with two or more nuclei; the failure of certain daughter chromosomes 

 to pull apart, leaving a chromatic bridge between the daughter nuclei; 

 the persistence of the nuclear membrane, with a division of the chromo- 

 somes by mitosis and of the nuclear vesicle by constriction. Conklin 

 concludes as a result of his many observations and an examination of 

 the evidence offered by others, that there is not known a single conclusive 

 case of true amitosis in a normally differentiating cell, and that all attacks 



