370 Mr. W.S. Perrin. On the [May 1, 
regarded as consisting of two parts, a central rod-like karyosom and a peri- 
pheral mass of chromatin, which in the normal resting nucleus masks the 
karyosom. 
An undulating membrane may or may not be present, the variability of 
this structure being particularly striking. When present it is wound spirally 
round the body of the Trypanosome, extending to the same distance as the 
nucleus at the ends. In favourable specimens the undulating membrane can 
be seen at one end of the animal to be connected with the nucleus by a fine 
thread of substance, staining like chromatin (fig. 1, c). At the other end the 
nucleus is apparently not continuous with the undulating membrane. The 
edge of the membrane is thickened, and stains like chromatin. This feature, 
together with the fact that the edge of the membrane is connected at one end 
with the nuclear band, render it probable that the membrane, at any rate in 
part, is a development of the nucleus. Flagella and blepharoplast are absent. 
Motion takes place in either direction with equal facility, and the anterior 
and posterior ends cannot be distinguished. 
The indifferent forms undergo multiplication by longitudinal division within 
the substance of the style, and where this process has reached such a stage 
that the style is closely packed with the parasites, they commence to encyst 
at the periphery of the style, the cysts passing out from the gut into the sea 
to infect fresh hosts. Where the oyster is kept out of water, the indifferent 
forms either encyst or undergo continued multiplication by longitudinal 
division, whereby they suffer great diminution in thickness, becoming 1n many 
cases mere threads, scarcely visible under the very highest powers of the 
microscope. 
The Female Forms.—These are so named because, from a consideration of 
their structure and behaviour, it seems highly probable that they are the pre- 
cursors of the female gametes. They differ from the indifferent forms in their 
stouter build, thicker periplast and undulating membrane, and occasional 
presence of vacuoles. Structurally they grade into the indifferent forms, and 
it is only in their extreme state of development that the two modifications 
can be distinguished from one another. In their behaviour, when subjected 
to adverse conditions of existence, however, the females exhibit a striking 
difference to the indifferent forms. In the first place they are much more 
resistent, neither immediately undergoing encystment nor entering into a 
phase of accelerated reproductive activity on the initiation of unfavourable 
conditions of life; and in the second place, when encystment does at last 
occur, they afford evidences of a parthenogenetic process in their nuclear 
changes, evidences lacking in the encystment of the indifferent forms. From 
the above features of their structure and behaviour, these forms appear to 
