MITOSIS AND AMITOSIS. 403 



absorption of surrounding substances by the chromosome takes 

 place through this membrane by a process of dialysis. The 

 nuclear vesicle is most nearly spherical in form when it is largest 

 and when its contents are most fluid in character irregular or 

 lobulated nuclei are usually smaller and the nuclear contents 

 more dense (Figs. 1-6). Therefore the modifications of mitosis, 

 which prevent the union of chromosomes into a single vesicle, 

 act by modifying the walls of these vesicles so that they do not 

 readily unite and so that they do not readily absorb fluid 

 from the cytoplasm. 



II. AMITOTIC OR MITOTIC DIVISION OF NUCLEI WITHOUT 

 DIVISION OF CELL BODY AND SUBSEQUENT DIVISION 



OF SUCH BlNUCLEAR OR POLYNUCLEAR CELLS. 

 In the cleavage of Crepidula a binucleate or multinucleate 

 cell is invariably due, so far as I have observed, to a failure of 

 chromosomal vesicles to unite into a single vesicle. In other 

 cases, however, it is plain that elongated, constricted and bi- 

 partite nuclei have resulted from the constriction of a single 

 nuclear vesicle. In addition to numerous cases which have 

 been described by other investigators, I have myself studied 

 such cases in the egg-follicle cells of Gryllus (Conklin, 1903), 

 the liver cells of Porcellio (Conklin, 1897), as well as in some 

 muscle cells and connective tissue cells. In none of these cases, 

 however, is division of the nucleus followed by division of the 

 cell body. Although every follicle cell of Gryllus and every 

 liver cell of Porcellio shows the nucleus in some stage of amitosis, 

 and although many of these cells contain two entirely separate 

 nuclei, in no single instance have I ever seen a division of the 

 cell body separating these nuclear halves. 



Since these cases of amitosis occur in differentiated tissue cells 

 it may be assumed that the nuclei are not active in the further 

 differentiation of these cells; on the other hand their metabolic 

 activity is great and the nuclei are undoubtedly concerned in 

 this activity. It has been assumed that the division or lobula- 

 tion of such nuclei favors metabolic activity by increasing the 

 surface of the nuclei and bringing them into closer relation to 

 all of the cytoplasm of the cell, and this is probably true. Espe- 



