374 Mr. W.S. Perrin. On the [May 1, 
absence of a hard shell or tough membrane is probably correlated with the 
aquatic environment of the oyster, which would render only slight protection 
of the cyst contents necessary. 
Encystment of the Female Forms.—In all its general features this resembles 
that of the indifferent forms, the cysts alone being larger in correspondence 
with the larger size of the females themselves. In point of nuclear change, 
however, as above mentioned, important differences manifest themselves. 
When encystment is comparatively far advanced, and the majority of the cell 
contents have emerged from the periplast, two small masses of deeply staining 
nuclear substance, connected by a feebly staining thread, are to be observed in 
favourably stained specimens. 
ei oe 
1 ot 
Fig. 4.—Schematic representation of female form encysting. p., empty periplast. c., cyst 
in process of formation. k., karyosom. 
This thread, with its two terminal chromatin masses, I interpret as being 
the karyosom of the nuclear band, with its chromatin aggregated at each 
end. This karyosom may occupy various positions with regard to the rest of 
the nucleus, which is now condensed, but usually passes through it. The 
two terminal masses of chromatin now appear to divide two or more times, 
the products of division remaining always connected to one another by a 
colourless thread. Most of these daughter bodies degenerate, but two remain 
over, one at each end of the thread, and appear to conjugate with one another. 
The whole process recalls somewhat the nuclear changes of the partheno- 
genesis described by Schaudinn in the case of 7’rypanosoma noctuw. The fate 
of the karyosom after the conjugation, and of the main portion of the nucleus is 
difficult to trace, but both structures become indistinct and possibly diffused 
throughout the cyst protoplasm, giving rise to a chromidial condition similar 
to that described by R. Hertwig in the case of Actinospheriwm. 
Summary of the Life History. 
In summarising the main points in the life history of Trypanosoma balbianit 
it is seen that the whole of the developmental cycle with the exception 
of the growth of fresh individuals from the cysts, takes place in the gut of 
a single host. In the style the Trypanosomes undergo longitudinal division 
as the normal method of multiplication, and when the number has become 
