in the Seminal Fluid of lanthiaa. 431 



this may be my excuse for communicating my obsenations upon 

 these structures in their present imperfect state. 



Even with the naked eye we may observe in the seminal fluid 

 of lanthina 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-foiurth 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 aa 

 the cause of the rapid movements by which the structures pasa 

 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. At a 

 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 fluttering 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. 



