in the Seminal Fluid of lanthina, 431 
this may be my excuse for communicating my observations upon 
these structures in their present imperfect state. 
Even with the naked eye we may observe in the seminal fluid 
of Ianthina numerous white vermiform structures, which swim 
about briskly in it*, Their length is about 0°5 millim. (exclu- 
sive of the swimming-apparatus to be hereafter described). The 
lens enables us to distinguish, in the first place, two sharply sepa- 
rated divisions, which may be indicated, for the sake of brevity, 
as the head and tail. The head occupies about one-fourth of the 
total length; it is sometimes of a pretty regular conical form, 
sometimes furnished at its posterior thicker portion with irre- 
gular processes, and sometimes projects anteriorly in a double 
instead of a single point. It contains numerous granules of 
various sizes, with dark outlines, which render it rather opaque; 
no distinct membrane could be perceived surrounding it. The 
tail, about three times as long as the head, is anteriorly much 
narrower than the hinder margin of the head, but becomes gra- 
dually enlarged posteriorly, and terminates in a rounded end; 
it is almost completely opaque, and is densely clothed with deli- 
cate hairs about 0:03 millim. in length. These hairs are seen 
to move quickly, but do not strike regularly in the same direc- 
tion in the manner of cilia; on the contrary, they wave and 
mingle together irregularly, so that we cannot regard them as, 
the cause of the rapid movements by which the structures pass 
through the water in large curves. In this movement the head 
and tail appear to be dragged along like a heavy mass by some 
force lying beyond them; and this is, in fact, the case. Ata 
distance of nearly twice the length of the head from its apex it 
is preceded by a conical point, with delicate but clearly marked 
outlines, from which a perfectly transparent membrane waves 
down to about the middle of the head, like a flutterimg veil. 
Sometimes I could detect an extremely delicate longitudinal 
striation in this membrane. Posteriorly its outlines were evanes- 
cent, so that I could scarcely ever trace it to its hinder mar- 
gin: on one occasion only, in a young individual, I distinctly 
saw the hinder margin, at which the membrane appeared to 
separate into delicate fibres. Sometimes also a slender and not 
sharply defined cord could be traced from the anterior extremity 
of the head nearly to the conical point. Whether this undu- 
lating membrane forms a conical envelope connected with the 
head by a central free peduncle, or whether it spreads out flat 
and is immediately attached to the head, I cannot decide; for, 
just as I was turning my attention to this question, the black 
clouds of a rising storm robbed me of the light so indispensable 
* Probably not throughout the year: my observations were made in 
October, which would correspond with April in the Mediterranean. 
