D. L. MACKINNON 
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of the second flagellum. Thus there are comparatively few bi-flagellates 
seen (fig. 28); much the most common appearance is that in figs. 18 
and 19, where the daughter organisms are hanging end to end, the one 
with a long flagellum, and the other with no more than a short stump 
yet formed. During the splitting of the rhizoplast, the kineto-nucleus 
can be seen to undergo division. In the iron-haematoxylin preparations 
it frequently appears kidney-shaped or tri-lobed at this stage, but an 
attenuated dumb-bell shape is also seen. Within the kineto-nucleus in 
Giemsa preparations the central body can be seen dividing in dumb-bell 
fashion. I have never been able to make out any karyokinetic figures 
in the tropho-nucleus as stained with Giemsa: it stains a uniform dull 
red at this stage, or shows the same appearance as in the resting stage. 
With iron-haematoxylin, however, it can be seen that at a very early 
stage the karyosome becomes elongated in the direction of the long axis 
of the flagellate, and the nuclear boundaries become vague. Gradually 
the ends of the now dumb-bell shaped karyosome recede further and 
further from one another, until they are only connected by a very faintly- 
staining strand, which then breaks (figs. 21—24). I never saw any 
unequal division, but as the exceedingly rapid multiplication proceeds, 
it is not surprising that the daughter flagellates tend to get smaller and 
smaller in size. At a certain stage, possibly determined by “depression” 
following on long-continued multiplication, the organisms proceed to 
encyst. 
3. Post-flagellate. The attachment of the herpetomonad flagellates 
to the epithelium of the hind-gut, their rounding up to form “gregarine” 
stages and finally cysts, are processes that have often been described. 
I have little new to add, though it was very common to find the rectum 
of Neuroctena simply swarming with encysting herpetomonads. I would 
point out, however, that here, as elsewhere, iron-haematoxylin gives a 
very different picture from Giemsa (cf. figs. 34 and 37 with figs. 39 
and 40). The kineto-nucleus appears much smaller, and the nucleus, 
instead of staining diffusely or appearing to have all the chromatin 
concentrated around its margin, shows a distinct central karyosome 
surrounded by a clear space bounded by a nuclear membrane. The 
numerous “chromatoid” granules in the cytoplasm of Giemsa pre¬ 
parations are here practically absent. A word about the disappearance 
of the flagellum. In some species of Herpetomonas the flagellum is 
apparently “cast off” in the last stage of encystment: in others, the 
portion external to the cell fades away and is absorbed. In his account 
of H. muscae-domesticae, Prowazek (1904) speaks of the flagellum as 
17—2 
