142 
Entamoeba histolytica 
nucleus of E. histolytica in the cat is different in structure from that found in 
amoebae from the human intestines. 
Turning now to consider the details of nuclear division the account given 
is, I think, the first in which the change undergone by the karyosome is 
worked out with any degree of completeness. The division is a primitive one 
and broadly similar to that described by others, but the behaviour of the 
constituent parts of the karyosome, namety the plastin and chromatin, is 
peculiar and of interest. 
The extrusion of chromatin into the cytoplasm of the vegetative forms is 
also of interest. 
There is no trace of centrioles in the dividing nucleus, nor of the extra- 
nuclear centriole described by Elmassian: I conclude therefore that the 
announcement of their existence was due to errors of observation. 
Figures similar to those given by Elmassian of extra nuclear centrioles 
are commonly found, but in all cases the granules, superficially resembling 
centrioles, are found to be either small cocci, which have been ingested, or 
other cytoplasmic inclusions in no way connected with the nucleus. 
Nuclear changes have been described by Hartmann under the term 
nuclear cycle, but the significance and relation, which they bear to division, 
do not appear to have been clearly recognised by this observer. In his paper 
on E. histolytica he states that this cycle of the nucleus rarely occurs, a fact 
readily understood when it is remembered that the “histolytica 55 type of 
nucleus is one ready to divide. As regards the main outlines of the life history 
of the vegetative forms I am in agreement with the majority of workers, 
except that I have been unable to find evidence for reproduction other than 
binary fission in the vegetative amoebae. 
The general morphology of E. histolytica is so similar to that of E. ranarum 
that Dobell in 1914 suggested that the life history of the two parasites was 
probably almost identical. Further the differences between the two seemed 
to him so small that he considered it possible that they were one and the 
same species. To test this idea experiments were performed, which have 
been published in a recent number of Parasitology (1918). The result, however, 
was negative and Dobell concludes “that E. histolytica Schaudinn and 
E. ranarum Grassi are probably distinct species, and consequently the frog 
in all probability is not a reservoir of human amoebic dysentery.” I would, 
however, point out that there are a few morphological differences between 
the two forms, which render this view of their non-identity probable. 
The cytoplasm is similar, although in E. ranarum the ectoplasm and 
endoplasm are not distinctly marked off from each other. The nuclei of the 
vegetative forms are, however, dissimilar, thus in E. ranarum the nucleus is 
devoid of a karyosome. 
In the cysts extrusion of chromatin from the nucleus occurs and a karyo¬ 
some developes by the running together of granules. This karyosome is 
obviously different from that of E. histolytica. 
