THE RELATION BETWEEN AMITOSIS AND MITOSIS. 95 



occurred. Occasionally the margins of the two nuclei are the 

 last portions to separate (Fig. 16, a). The flattened surfaces are 

 undoubtedly soon lost after division. Some of the cases of sepa- 

 ration from one side show very clearly that the separated parts 

 of the surface begin to become convex before separation is com- 

 pleted (Fig. 5, c). 



The division of the cytoplasm also varies to some extent, but 

 is more difficult to observe since the cytoplasm is usually with- 

 out any sharply defined boundary. In some cases a constriction 

 of the cytoplasm follows the constriction of the nucleus (Figs. 3, 

 a ; "J,f, i ; 9, A, d ; 29, /;, etc.), and in others the nuclear divi- 

 sion may be completed before the cytoplasm shows any trace of 

 constriction. (Figs. 7, d, g ; 8, A, c, c, i; 11, A, b ; 14, A, b, 

 etc.). Occasionally nuclear and cytoplasmic division are appar- 

 ently almost simultaneous (Figs. 7, h, i ; 8, A, //, etc.). A few 

 cases have been noted where the division of the cytoplasm is 

 "endogenous." Such a case is shown in Fig. \i,A,a; and 

 another in Fig. 21, a. Such cases as Figs. 2, a ; 5, d, and 29, a, 

 seem to indicate that a " cell-plate " may sometimes be formed 

 across the cytoplasm, though after the appearance of a cell-plate 

 it is of course impossible to be absolutely certain that the two 

 cells are the product of a division. But the fact that the nuclei 

 with their surrounding areas of cytoplasm are usually isolated 

 renders it probable that such cases represent division. 



Not infrequently one part of the nucleus stains more deeply 

 than the other. In such cases the stain is uniformly distributed 

 in each part but the boundary line between the darker and lighter 

 portion is sharp. Figs. 7, b, 14, B, a, and 16, c, show cases of 

 this kind. This difference in staining is of some importance as 

 indicating that there are differences of some sort in the two 

 regions and probably also that the two are functioning more or 

 less independently. 



Occasionally a case of what appears to be an " endogenous" 

 division is found (Fig. 13, E). In such cases the nuclear plate or 

 new membrane does not appear as a simple partition but two dis- 

 tinct membranes more or less convex toward each other are 

 formed, while the old nuclear membrane appears to surround the 

 whole. Some cases of this sort of almost diagrammatic clearness 



