STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAX. 95 



finely fibrous, compact connective tissue (PI. XVII, fig. 3). The 

 chitinous penis is similar to that of Calicotylc, but is shorter and more 

 slender (PI. XVII, figs. 1 & 2 ; PI. XVIII, figs. 3 & 7), and is 

 somewhat spiral. Its base is dii'ectly applied to the termination 

 of the vas deferens, and lies enclosed in the tubular cavity of the 

 penis -with only its terminal part projecting into the genital atrium 

 under the usual circumstances. 



Tristonium and Epibdella — In these genera the chitinous penis 

 is entirely wanting, and in both, the penis is nearly alike in structure ns 

 well as in ]X)sition relative to the other parts of the genital organs. 

 Unlike all the genei'a hitherto described, the common genital 

 pore, or in some species the separate male and female openirigs. are 

 sittiated quite in the lateral part of the body, a little behind the left - 

 anterior sucker. The penis is an elongated, hollow, subconical body 

 projecting for the greater part of its whole length into the genital 

 atrium. The basal portion of the penis is separated from the suiTOund- 

 ing mesenchyma by a thin, dense layer of connective tissue which vivid- 

 ly takes up the stain. This layer is, however, absent for a certain 

 extent at the very base of the penis, so that here the substance of the 

 penis is directly continuous with the general mesenchyma of the body 

 (PL XXII, fig. 2). The cavity of the penis is tubular for the greater 

 part of its length, but at its base it is enlarged spherically and receives 

 the openings of the prostate glands. 



The substance of the penis is somewhat different in histological 

 structure in different species; but generally it consists of a loose, 

 reticulated, fibrous connective tissue (PI. XXII, fig. 4; PL XXIV, fig. 

 1). In those species the mesenchyma of which is more or less of a 

 syncytial nature, as Trist. simuituin, the meshes of the connective tissue 

 are filled with a granular substance ; but the fibrous element seems 

 always to preponderate in the penis (PI. XXII, fig. 4). Towards the 



