322 University of California Publications in Zoology [Vol.20 



that in the cyst. In Endaniocha coli Dohell found a typical spindle 

 in the first nuclear division of the enc.ysted amoeba, but he also states 

 that "the subsequent nuclear divisions are all similar, and resemble 

 those of Endamoeba histolytica." Of the latter amoeba he says, "I 

 do not consider the nuclear division of E nclamoeba histolytica to be a 

 regular mitosis. On the other hand, I cannot call it an amitosis. It 

 seems rather to belong to an intermediate category." Certain resem- 

 blances may be found in his figure 64, plate 4, to some which are 

 presented in this paper. 



In Councdkruvnia lafleuri (Kofoid and Swezy, 1921) the type of 

 mitosis is closely similar to that shown herewith for Endamoeba coli, 

 both having polar masses or centrosomes and an intradesmose. Coun- 

 cilmania lafleuri has, however, eight chromosomes, differing in this 

 respect from E ndwmoeba coli with its six chromosomes. 



The nuclear division of the active amoeboid phase of Endamoeba 

 coli has not as j'et been observed by any investigator. Free amoebae ' 

 with two nuclei are occasionally met with and in one case (pi. 31, 

 fig. 25) one with eight nuclei was seen. These are not common, how- 

 ever, and it is probable that binary fission is the general rule among 

 the active amoebae, and that it occurs before the organisms leave the 

 upper part of the large intestine. The individual shown in figure 25, 

 plate 31, may be one that has escaped from its ej'st without dividing, 

 but it is also possible that such somatellas are .sometimes formed with- 

 out encj'stment as well as in the cysts, as in the case of the pareisitie 

 flagellates, Giardia (Kofoid and Christiansen, 1915) and Trichomonas 

 (Kofoid and Swezy, 1915). 



The question of a division center or centrosome in the parasitic 

 amoebae is one about which conflicting opinions maj' be found in the 

 literature on the subject. Dobell (1919) found no structures which 

 he could regard as centrosomes in Endamoeba dysenteriae. In a brief 

 description of the division of Endami-oeba dysenteriae, Mathis and 

 Mercier (1916) find, however, that such structures are present. In 

 1917 the same authors figure division in Endamoeba legeri from 

 Maoacus as a mitosis with centrosome, spindle, and centrodesmose 

 (::^ intradesmose). The centrosome originates in the karyosome and, 

 as it divides, the two daughter centrosomes draw out between them 

 a slender, darkly staining thread, which we have called the intra- 

 desmose. The spindle fibers are formed between the centrosomes 

 within the niielear membrane (their figs. II, b-d, h). This method of 

 procedure is closely similar to that oiitlined above for Endamoeba 



