286 MONOGRAPH OF THE LABOULBENIACE^. 



In the present genus, the antheridium, or what I have taken to be that organ, lies just beside 

 the bases of the lower appendages, and has not been satisfactorily made out, owing to the small 

 size and lack of definition in the cells lying in this region. In C. rhyncostoma, what appears to 

 be the neck of the antheridium becomes enlarged, as the individual matures, and projects as a 

 conspicuous hook-like prominence from the angles between the perithecium and the appendage 

 (Plate XXVI, fig. 18). The character of the trichogyne is also a matter of uncertainty, and 

 although 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 " appendages " 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 perithecium 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 C. 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 

 perithecium are remarkable from the fact that they are not confined to any special cell or even 

 cell-series, being quite variable in position, as in C. paradoxus, C. append imlatus, C. spinigerus, 

 C. uncinatus and others. The appendages closely resemble those of Peyritschiella, and are very 

 slender and evanescent, being usually completely broken off in mature specimens, the blackened 

 bases alone remaining. The more or less dome-like cell which bears the terminal appendage is 

 identical with the similar cell which bears this appendage in the last-mentioned genus. 



Reference has already been made to the form of the foot, which is peculiar to this and the 

 succeeding genus, and seems undoubtedly designed to allow a greater freedom of motion 

 necessitated by the exigencies of life in the water on a rapidly moving host. The base of the 

 foot, by which alone it is attached to the host, is rather narrow and pointed, while the upper por- 

 tion is more or less rounded, and serves as a fulcrum on which the individual may roll from side 

 to side through a considerable arc. The remarkable constancy with which the different species 

 occur in definite positions has also been previously alluded to (p. 246) ; and, as will be seen, is 

 practically invariable in every instance. All the species are aquatic, and are, so far as known, 

 confined to hosts belonging to the family Dytiscidse. 



As in previous instances, the side bearing the perithecium is considered anterior, the lower 

 appendages are thus described as arising from the left side. It may be remarked in passing that 

 species credited to Connecticut only are undoubtedly as widely distributed as the others, this 

 being the only looality in which they have been carefully sought for. 



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