286 MONOGRAPH OF THE LABOULBENUCE^. 
In the present genus, the antheridium, or wliat I have taken to be that organ, lies just beside 
the bases of tlic lower ai)pendages, and has not been satisfactorily made out, owing to the small 
size cuid lack of definition in the cells lying in this region. In C. rhjjnco stoma, what appears to 
be the neck of the anthei-idium becomes enlarged, as the individual matures, and projects as a 
conspicuous hook-like proniincnce from the angles between tlie perithccium and the appendage 
(Plate XXVI, fig. 18). The character of the trichogyne is also a matter of uncertainty, and 
altliough I have definitely made out the carpogenic and trichophoric cells, the latter terminating 
close beside the supposed antheridium, I have been quite unable to determine whether one of the 
two " api)endagcs " was in reality a trichogyne or whether, as is more probable, the latter is 
reduced merely to a slightly inflated prominence. Owing to the minute size of a majority of 
the species, and the difficulty in obtaining material of young individuals, the determination of 
these matters is by no means easy, and involves an expenditure of time that I have been unable 
to afford. 
In other respects the structure of the members of the genus is well defined and remarkably 
constant ; although the perithccium is subject to curious variations of form, and the terminal 
portion of the receptacle, especially its terminal cell, is often so modified as to obscure its true 
structure. In 0. melanurus, for example, the terminal and the sub-terminal cells are, at maturity, 
opaque and indistinguishable, the former becoming proliferous below its original apex and 
developing a hook-like extremity, the insertion of the originally terminal appendage being 
turned to one side, and visible only as a slight prominence from its inner margin (Plate XXVI, 
fig. 19). A somewhat similar modification is seen in C. marginatus, in which the whole distal 
portion of the receptacle becomes blackened, and the terminal cell is similarly proliferous (Plate 
XXVI, figs. 20 and 21 ; Plate VIII, fig. 27). The curious outgrowths from the wall-cells of the 
ccll-8crics, being quite variable in position, as in 
C. undnatm and otiicrs. Tlie aunendaws clnapl 
fined 
C.a. 
rev 
slender and evanescent, being usually completely broken off in mature specimens, the blackened 
bases alone remaining. The move or less dome-liko cell which bears tho terminal appendage is 
idcimcal with the similar cell which bears this appendage in the last-menfioned genus. 
Eeferenee has already been made to the form of the foot, which is peculiar to this mul the 
sncceedmg genus, and seems undoubtedly designed to allow a greater freedom of motion 
necessitated by he exigencies of lite in the water on a rapidly moving host. Tho base of the 
oot, by wlueh alone ,t ,s attached to the host, is rather narrow and pointed, while the u 
pper po 
(p. 246) 
d 
.^ • ... , . , , ; "" "■ '"'^^ ^"" *J" ^vnicn tne inctividual may roll trom side 
cc ;, Tfi ; " "'f' T The remarkable constancy with which the different species 
occn „ definite positions has also been previously alluded to 
practically invariable in every instance. All the species are a 
confined to hosts belonging to the family Dytiscids. 
As in previous instances, the side bear'imr the nerltbnni,,™ ■ ■ , , . • ^i i 
aniiendiiroo o,-„ n i •, , . . " peritiiecium is considered anterior, the lower 
sS ed ed o Co?" ;^ T T'' '™'" ""= '^'* ''''■ '' ""^ ^^ — I^^O "' P^^'S '""^ 
di tl^en V tcalif; '";;"';"■" ""'""'"^'"■^ '^ "■^^••>' '^-'"'^"leJ a, the others, this 
ucm„ tlie only locality in which they have been carefully sou-ht for. 
