STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAN. 97 



muscle consists of a few fibre«, wliicli are attached to the base of the 

 penis n little towards one side. 



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

 ness of the ditt'erent layers of muscular fibres just described varies 

 according to the species. 



Under the usual circumstances tlie penis lies complctclv in the 

 genital atrium; but it is sometimes seen |)rojecting from the opening 

 of tlie atrium, wliidi is tlien thereby forcibly enlarged (PL XXTII, 

 fig. S). 



Oncliocotyle — In this genus the penis is very difterent from those 

 hitherto described, at least in its relation to other p:u'ts of the ^enital 

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

 indeed entirely wtuiting in this o-enus — or into a homoloofous ca^•itv. 

 but is constituted simjtly 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 ductm ejaculntoruiii 

 (PI. XA'I, hg. 7). This mass of connective tissue is, roughly speaking, 

 conical in sliape, and is separated from the surrounding mesenchyma 

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

 just as in Trisloiituin. lUit unlike what is seen in th-at species the sub- 

 stance of the perds consists of a strongly réfringent, somewhat yel- 

 lowish, structureless substance which does not stain with liaematoxylin, 

 but which is traversed bv more or less well staininir, 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 (PI. XV, fig. 10; PI. XVE, fig. 7). The diiclu.<i 

 ejaculatoriux makes munerous windings in the penis, and finally opens 

 into the uterus just before this opens to the exterior. 



Jxine, Hexacotyle, andjvlicrocotyle reticulata — Strictly speak- 

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



