1909. | BLOOD-PARASITES OF FRESHWATER FISHES. 27 
7. TRYPANOPLASMA KEYSSELITZI, sp. n. (Plate III. figs. 40-44; 
Plate IV. figs. 66-73.) 
The occurrence of a trypanoplasm in the Tench has been noted by 
Keysselitz (Arch. Protist. vii. p. 3), but the species has not been 
described in detail, so far as I am aware, or named. Since it 
appears to me to be a well-marked species characterised by several 
striking peculiarities of structure, I propose to name the trypano- 
plasm of the Tench Zrypanoplasma keysselitzi, in honour of 
Dr. Keysselitz, who was the first, I believe, to observe it. From 
the figure given, however, by Lithe (Mense’s Handbuch, 111. fig. 5, 
p. 85) of the trypanoplasm of the Carp, I think it possible that 
T’. keysselitzi may prove to be a synonym of 7’. cyprini Plehn. 
Trypanoplasma keysselitzi was found im all the tench examined 
by me at Sutton Broad, always in company with 7rypanosoma 
tince. In some of the tench examined it was very abundant. In 
one case I saw as many as four or five in a field (Zeiss Oc. 
Obj. D) in a drop of fresh blood under the coverslip. In other 
cases the parasites were scarcer, but in no case was I unable to 
find them. 
The trypanoplasms occur under two distinct forms : one smaller, 
which, as it is the most abundant, I will call the ordinary form 
(figs. 42, 43); the other, less common, I will refer to simply as 
the lar oe form (figs. 40, 41). The two forms are easily dis- 
tinguished in the living state in the fresh blood. In preparations 
they are seen to be distinguished not only by differences in size 
but also by points of structure. The posterior flagellum is con- 
tinued beyond the undulating membrane as a relatively very long 
free flagellum in the ordinary forms, but the free portion is quite 
short in the large forms. There are also differences in the nuclear 
structure, presently to be described, between the ordinary and the 
large forms, and by this feature the large forms can also be 
separated into two types. 
The cytoplasm is finely and densely granular, and in the large 
form opaque and deeply-staining, but it is relatively free from 
the coarse granules which are such a feature of 7. gurneyorum. 
In iron-hematoxylin preparations only a few coarse granules are 
to be seen, sometimes none at all. 
The two nuclei of this trypanoplasm are remarkable, in the 
first place, for being situated very close together. The tropho- 
nucleus, always placed at the edge of the undulating membrane, 
is never more than a short way behind the kinetonucleus, which 
it usually overlaps at the hinder end, and sometimes even the 
trophonucleus is opposite the middle of the kinetonucleus. The 
arrangement of the two nuclei gives this trypanoplasm a very 
characteristic figure and appearance. 
The trophonucleus shows well-marked variations of structure. 
In the ordinary forms, when stained with iron-hematoxylin, it is 
2 small oval clear space which contains two distinct karyosomes 
(figs. 70-72). These bodies may appear as small dots, looking 
like two granules of the cytoplasm, or they may be larger, but 
