132 
IMTTRIEL ROBERTSON. 
The drawings, being made from leeches in the earlier 
phase of period (2), do not show the long, slender Trypano- 
somes developed during period (3). This final stage of the 
Trypanosome is most stinking ; but it is, of course, a matter 
of chance to get a leech in this condition in nature. This 
year I only got one ; it was only slightly infected, and I ivas 
unfortunate in not getting fixed films. 
It will be convenient first to give an account of the Try- 
panosome phase as found in the intestine of the leech (figs. 
8 — 11), and then to give any points of interest in its develop- 
ment from the resting form. 
The protoplasm is finely and evenly granular without 
vacuoles; indications of alveolar structure can be detected 
in some specimens, but are not very conspicuous. Proto- 
plasmic inclusions are only occasionally present. 
The trophonucleus is composed of a large central karyo- 
some surrounded by a wide halo, which is in turn surrounded 
by a membi’ane.” Fine, but perfectly distinct, rays pass 
from the karyosome to the outer membrane. The karyosome 
is quite obviously made up of two substances, namely, the 
chromatin and an achromatic substance, in which the chro- 
matin lies embedded. This achromatic substance frequently 
receives the name of plastin, and, while this does not convey 
any very clear idea, it is nevertheless a convenient and useful 
term. In Delafield’s preparations the plastin stains a pale 
greyish-blue, in iron hfematoxylin it is brownish, and it takes 
the green colour in the Twort’s combination. The nature of 
the rays is a little obscure : they stain, as a rule, rather 
faintly with Delafield, but in some cases take the colour more 
deeply; Heidenhain shows them up black, but they wash out 
easily. I am iucliued to regard them as more of the nature 
of plastin, but they seem at times to carry chromatin. The 
membrane shows very often little condensations of chromatin- 
staining material at the points where the rays meet it. The 
membrane stains well with Delafield and also with fuchsin, 
likewise with Heidenhain, but washes out long before the 
karyosome. The condensations on the membrane appear to 
