302 
DORIS L. MACKINNON. 
Tlie Nucleus. 
The nucleus presents very different appearances according 
to the intensity of the staining. In badly differentiated 
individuals stained, with iron-haernatoxyliii it has the aspect 
figured and described by Hamburger, i. e. that of a pear- 
shaped body at the anterior end ot the organism, containing 
a voluminous karyosome. Better staining reveals a clear zone 
surrounding the karyosome, and sometimes containing a few 
grains of chromatin. Above this is a dark-staining cone- 
shaped area, in which lie a number of chromatin granules 
supported in a delicate reticulum. These structures are 
enclosed within a definite pear-shaped membrane, the upper 
borders of which touch the basal granules. This is the most 
usual aspect. Sometimes, however, the nucleus wanders from 
its anterior attachment, and appears as a sphere containing a 
karyosome, and surmounted by a group of extra-nuclear 
granules ; in this condition it is strikingly like the nucleus of 
the Monocercomonas that occurs abundantly alongside 
Poly mast ix. 
The pear-shaped nuclear apparatus presents a certain 
resemblance to the calyx and contained nucleus of 
Lophomonas. Certain of Janicki’s figures of Lophomonas 
blattarum, Stein, are very suggestive in this connection — 
I refer more particularly to figs. 2b, d and e on pi. vi of 
“ Untersuchungen an Parasitischen Flagellaten,^’ I (^Zeit- 
schrift f. Wissenschaft Zool.,^ 1910). There, within a cup- 
shaped area, limited by a membrane, lies a spherical nucleus, 
which contains an eccentric karyosome surrounded by a clear 
zone and surmounted by a dark-staining mass containing 
scattered chromatin granules. In Poly mas tix there is no 
trace of the collar ” and other circumnuclear structures, 
though the cytostome may bring in another complication. 
The Axostyle. 
My preparations of Poly mas tix show the presence of a 
feebly developed axostyle, which had been overlooked by 
