248 Description of the Plates. 



anterior half of the segment which is removed, than in this, 

 the posterior. 



f. Intromittent organ, essentially a specialization of the muscular 



ductus ejaculatorius. It is armed with spines, which favour 

 its retention in the vagina, in the act of self-impregnation 

 observable in these ' heautandrous"" hermaphrodites. It is 

 here figured as retracted and coiled up spirally ; it is figured 

 as protruded in Figure 3. 



g. Vagina dilating into an oval receptaculum seminis, before 



joining the duct of the two vitelligenous glands. The 

 vagina opens externally in the posterior half of a saucer-like 

 depression on one side of a segment ; in the anterior half of 

 each the male outlet is situated. The generative outlets are 

 similarly arranged in the Taenia cucumerina, a tapeworm 

 commonly found in the dog; and in the Taenia elliptica, a 

 tapeworm which infests the cat ; but the glandular organs 

 being double, the outlets are double also, and exist on both 

 lateral edges in each segment. In the Taenia medioca- 

 nellata of the human species, the common generative de- 

 pression is situated some way behind the middle of the 

 lateral border of each segment; in the Taenia solium it is 

 nearer to the middle line, whilst in Bothriocepliahis latus, 

 which, like the two tapeworms, infests the human subject, 

 both orifices are situated on one of the flat aspects of the 

 segment they belong to. In other species, the male orifice 

 may be situated on the edge, and the female on the flat 

 aspect of each segment. 

 A segment with the generative organs in the condition here 

 figured, would be found in either Taenia solium or Taenia 

 onediocanellata, the two common human tapeworms, at about 

 the 450th segment counting backwards from the head ; and 

 the segments would assume the appearance given in Figures 

 3 and 4, after about 300 more segments in Taenia solium^ 

 and 360 to 400 in Taenia mediocanellata. 



