158 ENTOZOA. 



process. The outlets of tliese organs are placed side by side, in 

 tlie middle line, and a little above the ventral sucker ; the male 

 apparatus terminating externally by a conspicuous intromittent 

 organ or penis. This appendage is very commonly found pro- 

 truded in the dead fluke, being always, in this case, more or less 

 curved upon itself in a spiral manner. The organ itself consists of 

 layers of longitudinal and transverse muscular fibres, surrounding 

 a central mass of highly contractile parenchymatous cellules. Its 

 extremity is lobed and imperforate, the included seminal duct 

 (ductus ejaculatorius) terminating, according to Simonds, on its 

 surface, near a point corresponding with the commencement of the 

 lower third of the organ. Not having myself seen the alleged 

 opening at the extremity of the organ, I am inclined to believe that 

 Mr. Simonds' description of the generative appendage is, in this 

 particular, more correct than any other that has appeared. In the 

 retracted condition the penis is lodged within a distinct pouch or 

 sac, its position being indicated only by a triangular depression and 

 sHght fulness of the surrounding parts. The integument of the 

 penis is manifestly a production of the ordinary epidermis and 

 cuticular covering, and like the latter is furnished with a number 

 of minute spines. These frequently drop off, causing the organ 

 to appear naked. The pouch or cirrhus-sac not only encloses a 

 penis, during its retractation, but also a large flask- shaped seminal 

 receptacle, in which one may observe a dense granular mass, 

 consisting of multitudes of spermatozoa. At the lower part of the 

 sac the receptaculum seminis receives the two vasa deferentia, which 

 combine to form a single channel near their point of junction with 

 the receptacle (Plate XI., Fig. 6). These filamentary ducts are of 

 unequal length, and distinct throughout the greater part of their 

 course, which commences, in either case, at a point where the 

 seminiferous tubes of the testes coalesce. In this animal the testes 

 are exceedingly peculiar ; for instead of forming two large globular 

 masses (as usually happens in the flukes), they are split up, as it 

 were, into a multitude of very narrow vermiform tubes, being 



