304 University of California Publications in Zoology [Vol. 20 



two tj'pes are quite distinct and that the type in the cells under sus- 

 picion is distinctly that of the rhizopod rather than that of the mam- 

 malian or human cell. 



Two human cells from the lymph gland are shown in the metaphase 

 and anaphase of mitosis in figures 1 and 2. 



The human cell at mitosis is characterized by three fundamental 

 structural features which are common to mammalian, if not to meta- 

 zoan cells, at mitosis. These are, first, the entire disappearance of 

 all traces of the nuclear membrane. This leaves the spindle of the 

 dividing cell with lis equatorial (fig. 1) or divided (fig. 2) group of 

 chromosomes exposed free in the enveloping cytoplasm. In the com- 

 parable stages in the mitosis of amoeba (figs. 6 and 7), the whole 

 spindle is contained within the persistent nuclear membrane. This 

 membrane can be distinctly followed in focussing as a slightly stained 

 wall surrounding the spindle. The spindle lies within it, its spindle 

 fibers being few (fig. 6) in comparison with the many fibers of the 

 human spindle (figs. 1 and 2) and lightly stained. The centrosomes 

 are minute dots at the poles (fig. 6) within the nuclear membrane 

 of the dividing nucleus of amoeba. 



A second point of difference is the absence in the human spindle 

 during the period of late prophase to the close of the anaphase of a 

 deeply staining strand joining the centrosomes which we (1921) have 

 called the intradesmose. The intradesmose is formed from the 

 parental centrosome and as this divides and the resulting daughter 

 centrosomes move to the poles of the spindle, a deeply staining sub- 

 stance similar, in iron haematoxylin, to that in the polar masses which 

 constitute or contain the centrosomes, is spun out in a meridional 

 thread often applied to the inner face of the nuclear membrane. If 

 heavily decolorized, this is destained. If laterally located, it may be 

 difficult to detect. In favorable material (fig. 7) it is clearly seen. 

 This structure has been found by us in dividing nuclei in the intestinal 

 cysts of Endamoeba dysenteriae (not yet published) , in E. caU (Swezy, 

 1922, in press) and in Cowncilmani'a lafleuri (Kofoid and Swezy, 

 1921). It corresponds to the extranuclear paradesmose of the flagel- 

 lates, and to the axial strand of linin fibers in the mitotic spindle of 

 the dividing metazoan cell. In the dividing human cells, from the 

 lymph glands of Hodgkin's disease, no structure such as the intrades- 

 mose can be found. In fact, none is known in cells of mammals, nor, 

 in so far as we know, in an.y metazoan cells. In the Protozoa, it 

 occurs in the Rhizopoda. 



