STUDIES ON THE ECTOPARASITIC TREMATODES OF JAPAN. 97 



muscle consists of ,1 few fibres, which are attached to the base of the 

 penis a httle towards one side. 



It is perhaps hardly necessary to remark that the relative thick- 

 ness of the different layers of muscular fibres just described varies 

 according to the species. 



Under the usual circumstances the penis lies completely in the 

 genital atrium; but it is sometimes seen projecting from the opening 

 of the atrium, which is then thereby forcibly enlarged (PI. XXIII, 

 fig. 8). 



Onchocotyle — In this genus the penis is very different from those 

 hitherto described, at least ia its relation to other parts of the genital 

 ducts. It does not, namely, project into a genital atrium — this is 

 indeed entirely wanting in this genus — or into a homologous ca^'ity, 

 but is constituted simply by a mass of peculiar connective tissue around 

 the terminal portion of the vas deferens, which therefore, consistently 

 with our nomenclature, is to be called the ductus ejaculatorius 

 (PI. XVI, fig. 7). This mass of connective tissue is, roughly speaking, 

 conical in shape, and is separated from the surrounding mesenchyma 

 by a thin layer of well staining, dense, fibrous connective tissue, 

 just as in Tnstomum. But unlike what is seen in that species the sub- 

 stance of the penis consists of a strongly refi'ingent, somewhat yel- 

 lowish, structureless substance which does not stain with haematoxylin, 

 but which is traversed by more or less well staining, reticulated fibres. 

 It contains a small number of nuclei which are perfectly like those of 

 the surrounding mesenchyma, and are sometimes surrounded by a 

 granular protoplasm (PL XV, fig. 10; PL XVI, fig. 7). The cliictm 

 ejaculatorius makes numerous windings in the penis, and finally opens 

 into the uterus just before this opens to the extei'ior. 



Jxine, Hexacotyle, and Microcotyle reticulata— Strictly speak- 

 ing there is no separate organ that can be called penis in these forms ; 



