STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAN. ,S5 



Each testis is separated from its Deigliljours by 'a more or less thin 

 layer of mesenchyiiia, which in this region assumes the character of 

 reticulated, fibrous counective tissue (Pi. V, fig. 7 ; PJ. XI, fig. o ; 

 ?1. XXIII, fig. 7 ; rj. XXIV, fig. 2); and is usually destitute of 

 any distinct epithelium. The testes are also traversed by the dorso- 

 ventral muscular fibres ; but the greater part of these pass between 

 them through the mesenchymatous septa just mentioned. The con- 

 tents of the testes consist of sperm cells in various stages of develop- 

 ment, scattered witliout any regularity. In some species, as in 

 Dididopliora scssiUs (PI. XI, fig. 5), I have often (observed cells with 

 larofe nucleus ari-jm"'ed in a sin^-le laver on. the wail of the testis ; 

 but tliese seemed not to form ii perma.nent epithelium. For, they 

 were only loosely a.pposed to the mesenchyma, and in m:uiy testes, 

 especiadly in those in which the greater part of the sperm cells had 

 finished their development, they were wholly absent. A general view 

 of the contents of the testes may be obtained from fig. 7, PI. Y, figs. 3 

 & 5, PL XI, fig. 7, PI. XXIII, and fig. 2, PI. XXIV. The most 

 conspicuous elements besides the already developed spermatozoa are the 

 groups of large nuclei containing a certain number (how many I have 

 not been able to make out with s;itisfacti(Hi) oï chnjmacin granules, the 

 interspaces of which stain uniformly but far more weakly with 

 haematoxvlin, and the cells of large dimensions usu;dly more or less 

 of a sDherical form, with a simrle, lonir thread of chromatin formino' an 

 irregular .skein, or witli numerous, more or less lozenge-shaped pieces 

 of chromatin. The large nuclei just mentioned were usually sur- 

 rounded by such :i scanty layer of protophism as almost to look naked. 

 Besides these there are also groups of much smadler nuclei imbedded 

 together in a unifrrui mass of very finely granular protoplasm, which 

 sometimes sliowed traces of separation corresponding to each nucleus. 



The various elements above characterised are obviously stages in 



