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unequal division is common. Such a case is that of Plate III, Fig. 4 b, 
where a thin cell, containing two minute dark-staining granules and 
an anterior vacuole, is being split off from the side of an encysting 
individual. 
In one flea the flagellates presented a somewhat different appearance 
(Plate III, Fig. 4 a and 6). They were shorter and broader (15/a x 3/a, 
on an average) and less attenuated posteriorly; but the main difference 
consisted in the distribution of the chromatin, which crowded the 
cytoplasm in irregular strings and granules. These stained deep red to 
purplish, and it was often impossible to distinguish the blepharoplast. 
The nucleus, on the other hand, stained with great difficulty, and 
generally appeared as a pale area surrounded by “chromidia” (?). 
(3) Post-flagellates. These were found mainly in the rectum and 
occur singly or in groups (Plate III, Fig. 8). The parasites shorten and 
broaden, becoming pear-shaped and finally round (Plate III, Figs. 5 to 
11). They also increase considerably in volume (5/a x 4/a is an average 
measurement). The nucleus undergoes interesting changes, the meaning 
of which is not at all clear. In the earlier stages of encystment it 
swells out (2/a), and no longer stains uniformly: the general mass is 
pale pinkish-red, with deeply-staining chromatin collected round the 
borders, and 'connected by irregular granules with a central mass 
(karyosome ?) (Plate III, Figs. 7 and 8). In some instances where 
the nucleus appears to be undergoing division, the chromatin is collected 
into a uniformly-staining mass, which becomes dumb-bell-like and 
divides by simple constriction (Plate III, Fig. 14 a). Disintegration 
of the nucleus may occur. Fig. 12 shows a cyst in which the 
nucleus has taken on a blurred and fragmentary appearance. In 
Fig. 13 the whole nuclear content is being scattered into the cytoplasm 
as chromidia. Finally, there are a few individuals which have apparently 
lost all but a trace of the nucleus—such forms are shown in Fig. 14 b 
and Fig. 15. The cysts that have completely rounded up generally show 
an evenly-staining nucleus of smaller size than in the initial stages of 
encystment, and with the chromatin peripherally disposed (Fig. 11). 
The blepharoplast becomes broader and stains more lightly—sometimes 
the nucleus and the blepharoplast stain the same shade. Its position 
in the cell is variable, but in the pear-shaped forms it usually lies against 
the nucleus, either anterior or to one side. In the final stage of rounding- 
up it may be widely separated from the nucleus (Fig. 11). Occasionally 
cysts are seen in which the blepharoplast is undergoing repeated division 
(Fig. 12). This may reach a condition in which the blepharoplast is 
19—2 
