1016 MR. F. E. BEDDARD ON 



is seen to open into an invaginated sac wliicli lies pushed into the 

 solid core of the cirrus sac, as is shown in the text-figure accom- 

 panying this description. This sac is irregular in form with 

 crumpled walls, and it is surrounded by a layer of particularly 

 stout muscular fibres, which lie therefore within the cirrus sac 

 and form a diiferentiated portion of its core. These muscular 

 fibres lie loosely round the invaginated sac. The wall of the 

 latter is rather thickened to form a pad lying on the anterior 

 side, and close to this the cirrus opens into it, their cavities 

 becoming continuous. The opening into the sac is opposite to 

 the pad, and therefore on the posterior side of the sac. 



The cirrus sac does not open directly on to the exterior, but 

 through a genital cloaca which is itself much complicated. A 

 horizontal section through the whole structui^e is represented in 

 text-fig. 215. The genital cloaca may be divided into three or 

 foiir regions ; the invaginated penis (as we may term the in- 

 and evaginable sac into which the cirrus opens) is continuous 

 with a wide but narrow cavity of quite as great a diameter 

 (antero-posterior) as the cirrus sac itself, but very nai-row from 

 side to side. After this comes a tubular cavity surrounded 

 by a very thick layer of cii-cular fibres which are perfoi-ated, as 

 already mentioned, on the posterior side by the vagina which 

 here enters the genital cloaca. In horizontal sections such as that 

 represented in text-fig. 215, this layer of miiscles appears as two 

 strong muscular pads, that on the posterior side being longer 

 from side to side than the one opposite. After this the canal 

 Avidens a little for the terminal part of its course and its walls 

 are rather crumpled, there being a pai'ticularly deep recess 

 immediately after the sphincter region which precedes it. A 

 considerable portion of the cirrus sac can be evaginated, sometimes^ 

 more and sometimes less. These differences also are shown in 

 text-figure 215. In some cases only the anterior side of the 

 cirrus sac is protruded, which in such a case barely reaches 

 the external orifice of the genital canal. In other cases 

 much more is protruded, and the cirrus itself is drawn down 

 into this penial protrusion Avhich extends well beyond the 

 external orifice. In this latter case, however, which represents 

 the extreme of what I have seen in my sections, the actual opening 

 of the vas deferens is not at the tip of the protruded penis, but 

 at the side and within the genital canal. I may not perhaps have 

 seen instances of extreme protrusion. It is noteworthy that the 

 orifice of the vas deferens is on the posterior side of the penis and 

 thus corresponds to the vaginal orifice. Possibly a complete 

 extrusion of the penis takes place in cases of cross-fertilisation. 



The following are the general characters of this species * : — 



Head quite imarmed, of rather large size and with four vnnrmed 

 suckers. Strobilisation begins at once, there being no " necTc " ; tlie 

 first two or three strobila ivider than those which immed/mtely folJciv 



* I do liot attempt to discriminate between generic and specific characters. 



