M. W. Jepps and C. Dobell 
361 
E. histolytica, because of its very different size and structure. And 
although “Entamoeba’' nana might from its size seem a plausible guess, 
a comparison of the nuclei of this species mth those of Dientamoeba 
renders such a suggestion highly improbable; and the invariable absence 
of cysts from the faeces of persons infected with the latter alone, makes 
it impossible. It is clear therefore that, whatever the correct interpre¬ 
tation of the binucleate condition of Dientamoeba may be, we are dealing 
with an organism which is different from those hitherto described. 
The interpretation which we put upon our findings is as follows. 
Dientamoeba is an amoeba which, when fully differentiated, possesses 
two nuclei. It appears to us probable that when an adult binucleate 
individual divides, it undergoes fission of the cytoplasm only, so as to 
form two small uninucleate individuals. The nucleus in each of these 
undergoes division into two at some time, which is variable, during the 
period of growth into the adult form. 
Such a hypothesis will square with all our observed facts—with the 
preponderance of binucleate individuals in the population, and with the 
occurrence of binucleate and uninucleate amoebae of all sizes. Unfortu¬ 
nately we have found very few amoebae indeed in which nuclear division 
appears to be occurring. One such individual is shown in Plate VII, 
fig. 15, but from the very few nuclei that we have seen in division, we 
are unable to describe the process in detail. All the dividing nuclei have 
been seen in uninucleate individuals. We have never seen a binucleate 
individual with its nuclei dividing simultaneously, although we have 
seen two amoebae each containing four nuclei. We regard these quadri- 
nucleate individuals as abnormal forms, similar to the binucleate and 
multinucleate individuals which occur occasionally in cultures of some 
of the small free-living amoebae resembling “Amoeba Umax,” or to the 
binucleate individuals sometimes seen in the three uninucleate intestinal 
amoebae of man. Such division stages as we have seen in Dientainoeba 
agree, therefore, with the interpretation outlined above. 
Several binucleate amoebae are, of course, already known. The first, 
“Amoeba” binucleata, was described by Gruber (1885) from fresh water, 
and studied later by Schaudinn (1895), who described its method of 
nuclear division. It may be remarked that this organism can hardly be 
left in the genus Amoeba, though its transference by Doflein (1909) and 
Penard to the genus Pelomyxa appears to us equally impossible, and we 
believe that a new generic name must ultimately be assigned to it^. 
1 Alexeieff (1912, 1912 a) lias proposed to place it, wth other forms, in the genus 
Hartmannella AlexeiefE {=Eartmannia Alex. 1912, preoccupied). We cannot agree with 
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