258 ANIMAL PARASITES. 



spermatozoids in the vesicle a, I shall regard it as a ves. sem. 

 interna, although I confess that even from the colour of this 

 structure, I can hardly suppose that it is a vesica seminalis interior. 

 As regards the colour, all the seminiferous organs, and therefore 

 even the above-mentioned dilatations of the testicles, are brownish- 

 red, and, in fact, lighter or darker according to the calibre and 

 number of the free filaments. 



It still remains to furnish the microscopic proof that the 

 convolutions already described by Mehlis as testicles are really 

 those organs. If we make a fine transverse incision in the 

 middle of the animal and far behind the point of uniob of the 

 vitelligenes, we shall also have removed therewith some of the 

 upper convolutions, and may easily isolate them. But at the 

 cut surfaces of these convolutions innumerable seminal filaments 

 flow out, and I have attentively observed this singular spectacle 

 for a long time. Thus we observe simple, hyaline cells ; then 

 stellate ones, consisting of five cells ; then some in which caudated 

 cells, as it were, protrude from these cells, and also free bundles 

 of fine long seminal filaments and individual isolated filaments. 



For the last investigations I of course made use of fresh, living 

 Distoma, and, as the medium in which I examined them, sugar 

 and water. For the investigation of the anatomical arrangement 

 of the separate portions of the genital system, I employed the 

 process, above described under the section " vagina," of scalding 

 the animals with boiling water — a process which merits being 

 more brought into use in the examination of various lower 

 animals. 



b. The sac of the pe?iis (cirrhus-pouch) itself, and the whole of 

 the reproductive organs connected with it, lie immediately on the 

 anterior surface of the ventral sucker, and open towards the ven- 

 tral surface. Here we clearly distinguish the oval, or, more cor- 

 rectly, retort-shaped end, formed by the true penis-sac, a swollen 

 white mass when examined with the naked eye, dingy blackish-red 

 under the microscope, and containing immense numbers of sper- 

 matozoa, which, when they can be examined in a more isolated 

 condition, exhibit a lively swarming. Anteriorly this penis- 

 sac passes into a distinctly recognisable, contorted, ductus 

 ejaculatorius, with a double outline, in which I once observed 

 distinct peristaltic movements for several minutes after taking the 

 whole apparatus out of the body of the living animal. Thus, 

 sometimes one wall contracted at the bending of the canal, and 



