BINUCLEATE CELLS IX TISSIE CLLTUHES. 87 



through their own movements (as they have been described by Lewis and Lewis, 

 1915), since they are typically found between the nuclear parts when these are 

 separated to any extent (fig. 9), and a strand of mitochondria may even be seen 

 Ijang across the constricted isthmus of the nucleus, when this has not become com- 

 pletely divided (figs. 6 and 8) . This position of the centrosphere and mitochondria 

 undoubtedly seems to have some significance in sejiaration of the nucleus, and is 

 seen even where the nucleus is dividing irregularly, as in figures 48 to 58. 



The relation of the Netzapparat of Deineka(1912,fig.3jto the nucleus is similar 

 to that of the centrosphere as just described, viz, it is found in the cleft separating 

 the nuclear portions. This author, however, does not ascribe to it any function in 

 nuclear separation. He believes that it surrounds the centrosome. 



The position of the centrosphere and mitochondria may, of course, be without 

 significance, so far as the actual division of the nucleus is concerned, and it is possible 

 that the relationship of these cytoplasmic bodies to the amitotic nucleus is purely 

 fortuitous, or, at most, occasioned through their adjustment to conditions of intra- 

 cellular pressure. The occasional absence of the centrosphere from the cleft (once 

 in each 50 cases as determined by counts) and the presence of a cleft opposite the 

 one in which the centrosphere is found are points which count against this second 

 hypothesis. Again, not all nuclei, in which the centrosphere appears in a concavity 

 on one side, divide directly; indeed, this relationship of centrosphere and nucleus 

 has frequently been noted and illustrated in cells developing, without nuclear 

 amitosis, in their normal environment. It would seem, therefore, that this rela- 

 tionship, of itself, can not bring about nuclear amitosis. 



In no case has there been noted a ring-shaped centrosjihere, like that described 

 by Meves (1891), which encircles the constricted zone in the dumb-bell-shaped, 

 amitotically dividing nucleus. 



The centrosphere and mitochondria may be assumed to act in another way in 

 accomplishing direct division of the nucleus, viz, by bringing about a change in the 

 surface tension of the area of the nucleus to which they are ojjposed, through the 

 elaboration of a chemical substance, and it may be possible to e.xplain direct division 

 of the nucleus upon some such hypothesis as that used by Robertson (1909, 1911, 

 and 1913) to account for division of the cell in mitosis, viz, that there is produced 

 in the region of cleavage some chemical substance which lowers the surface tension, 

 such as soap, and that there results, in consequence, a streaming of protoplasm 

 away from the equator, leading to separation of the cell. Robertson postulates a 

 cholin-fatty acid soap, the cholin being derived from the splitting-up of lecithin. 

 Since it has been shown that mitochondria are lecithinoid bodies (Cowdry, 1914, 

 J). 18) it is not beyond the range of possibihty to assume that they may act in the 

 formation of a cholin soap. Indeed, the relation of mitochondria to the production 

 of chohn in nerve-cells has recently been discussed by Cowdry (1915). The position 

 of the mitochondria, lying across the zone of nuclear constriction (fig. 8) is eminently 

 favorable for the action of such a soap, should it be formed there. 



A third theory to account for direct division of the nucleus is based upon the 

 assumption that some intranuclear change inaugurates the process. As long ago 



