404 EDWIN G. CONKLIN. 



cially in the case of elongated muscle cells the division of the 

 nucleus and the distribution of the daughter nuclei along the 

 length of the fiber must facilitate interaction between nucleus 

 and cytoplasm, and the same is true, though perhaps to a smaller 

 extent, in gland cells and egg-follicle cells. 



Dahlgren and Kepner (1908) hold that the very numerous 

 amitoses in the striated muscle cells of the embryo fish, Catos- 

 tomus, may be followed in some instances by the division of the 

 muscle cell. But since the plane of nuclear division is always 

 transverse to the fiber, while the plane of cell division is always 

 longitudinal, it could not be affirmed that the cell divisions in 

 this case correspond to the nuclear divisions. But even if 

 amitoses may be followed by division of the cell body in these 

 cases, it must not be forgotten that all these cells are fully differ- 

 entiated and according to the chromosome theory the nucleus 

 has already performed its differentiating functions w r hile its 

 further function in the fully differentiated cell is probably purely 

 trophic. 



Many observations and experiments demonstrate that the 

 nucleus is concerned in the two functions (i) of differentiation or 

 regulation and (2) of metabolism; the work of Gruber (1886), 

 R. Hertwig (1898), Heidenhain (1894), Henneguy (1896), 

 Conklin (1902) et al. indicates that the chromosomes or basi- 

 chromatin are particularly concerned with the former, the 

 oxychromatin or achromatin with the latter. It is a significant 

 fact that chromosomes divide only by mitosis and Boveri (1908) 

 has shown that a complete set of chromosomes is necessary to 

 normal differentiation. On the other hand oxychromatin and 

 achromatin divide only by amitosis even in cases of mitotic 

 division of the chromosomes. The significance of these facts 

 seems to have been missed not only by those who maintain the 

 equivalence of mitosis and amitosis, but also by Weismann and 

 his followers who assumed that in embryonic differentiation 

 there is a differential division of chromosomes and a "disinte- 

 gration of the germ plasm" with segregation of particular factors 

 in particular cells. For if individual chromosomes differ in 

 hereditary potencies, every division by amitosis must be a 

 differential one, while on the other hand every typical mitotic 



