1923] Swezy: Mitosis in E iidamoeba CoU 315 



nuclei in the majority of the cj'sts; those made later contained prac- 

 tical!}' no cysts with dividing nuclei but a relatively greater number 

 of eight-nucleated cysts. This would seem to indicate that division 

 proceeded normally in this case. The only good mitotic figures were 

 found on the firet set of slides, with the exception of that shown in 

 figure 23, plate 31, which was taken from a .set of slides made after 

 the stool had been standing in the laboratory for twenty-four hours. 

 The fact, however, that this single stool was the only one among 

 several thousands which gave an abundance of division forms indicates 

 the rarity of the occurrence of mitosis in cysts in stools examined in 

 the ordinary manner. The fortunate coincidence of discharge during 

 a phase of normal nuclear multiplication and prompt access to the 

 material and its early fixation has made this study possible. 



ACKNOWLEDGMENTS 



The work which forms the basis of the following study was done 

 while the author held the Sarah Berliner Research Fellowship, and 

 it is with pleasure that the indebtedness of the author to this founda- 

 tion is acknowledged. The author is also greatly indebted to Professor 

 Charles Atwood Kofoid for the abundant resources of his laboratory 

 at the University of California which have been placed at her disposal. 



MORPHOLOGY 



The active amoeboid stages of Endamoeba coli may be readily dis- 

 tinguished from Councilmania lafleuri, in both fresh and stained 

 material, by granular pseudopods and lack of clearly marked ecto- 

 plasm, as well as by more sluggish movements in the living forms. 

 The cysts are distinguished on careful examination of the karj^osome 

 when unstained or in iodine-eosin, and may be more readily differ- 

 entiated in fixed and stained preparations. These differences have 

 been summed up in a recent paper (Kofoid and Swezy, 1921) and 

 need not be repeated here, except to point out the fact that they may, 

 in some cysts, be almost entirely obscured during certain stages of 

 the process of mitosis, such as the early prophase and late telophase, 

 when chromosomes cannot be counted in the encysted amoebae. The 

 same fact will probably hold true of division in the active forms of 

 these two species, but, thus far, division in the active amoebae has not 

 been found in our material. More data are needed on this point. 



