M. Koidzumi 
285 
wall at several points. As remarked above, the number of peaks visible on 
the nucleus is variable, depending on the condition of the body, and it is 
doubtful whether the points of attachment of the nucleus are constant in 
position or not. 
The position and the shape of the nucleus seem to be quite different in 
the American and Southern European species of Pyrsonympha. In these the 
nucleus assumes an oval or an elliptical shape, and is situated away from the 
anterior tip of the body and not so closely connected with the axial filament. 
No description of the attachments of the nucleus to other parts of the body 
are to be found in the works of previous authors (Leidy, Porter, Grassi, 
Comes, and Zulueta). Some of the figures given by them, however, seem to 
indicate the existence of a structure similar to, but less developed than, that 
of our forms. 
The internal structure of the nucleus of Pyrsonympha is quite different 
from that of the trichonymphids. It is of a type resembling that of the 
gregarines and coccidia, consisting of a fine and distinct achromatic network 
with minute chromatin granules, and one, two, or more large chromatic 
bodies, or karyosomes, situated centrally and usually surrounded by a clear 
space. The chromatic body has a vacuolate structure, and closely resembles 
the karyosome of gregarines and coccidia, but is often somewhat rough in its 
contour (PI. XIY, figs. 54-56). 
The endoplasm appears more or less homogeneous and somewhat compact 
in consistency, and rather closely resembles that of Microspironympha and 
Holomastigotes. In the small forms the endoplasm appears rather clear; but 
