1922] Swezy: Mitosis in Enclamoeba Coli 321 



to be closely similar, if not identical, in the two-, four-, and eight-cell 

 stages. There is considerable decrease in actual size of the nuclei 

 with each successive division (pi. 31, fig. 23), giving to the cysts with 

 eight or more nuclei a greater disproportion between the size of the 

 cyst and that of the nuclei (pi. 31, fig. 22) than may be found in the 

 earlier stages, where the nuclei are relatively large (pi. 29, fig. 2). 

 Thus in the one- and two-cell stage the diameter of the nucleus may 

 be equal to one-third that of the cyst, while in the eight-cell stage the 

 diameter of the nucleus may be one-sixth, or even less than that, of 

 the cyst. 



Division of the protoplasmic body has not been observed in Enda- 

 nioeba coli, either in the active or in the encysted amoeba. In the 

 latter case it may well be that it is delayed until after leaving the 

 body of the host and entering a new one. Figure 25, plate 31, would 

 suggest that the multinucleate somatella is released from the cyst 

 before dividing into the individual amoebas, though this may be the 

 result of repeated divisions in the active amoeba without plasmotomy 

 intei-vening, as individuals with two or more nuclei may occasionally 

 be observed. 



DISCUSSION 



The literature on the subject of division in the parasitic amoebae 

 is filled with confusion and misinterpretations, the result, largely, of 

 generalizations on too scanty data. The earlier conceptions of this 

 process as a "simple amitosis" were, perhaps, unavoidable, but with 

 the constantly growing knowledge of the types of mitosis that may be 

 found in the Protozoa at the present time, modifications of these 

 earlier conclusions are to be expected as the result of further investi- 

 gations along this line. It seems very probable that simple amitosis 

 is as rare in the higher Protozoa as in the Metazoa. 



In Dobell's recent discussion (1919) of the nuclear behavior of 

 the human intestinal amoebae, he gives a number of division figures 

 of Endamoeba dysenteriae, taken from active amoebae from intestinal 

 ulcers of cats experimentally infected with human amoebae. The 

 type of division shown in these figures differs somewhat from that 

 shown herewith for Endamoeba coli, and it may be that the alien 

 environment which the human amoebae find in the eat has produced 

 some modifications which are not present when the amoebae occupy 

 their normal habitat, or that division in the active form differs from 



