STERELMINTHA. 91 



nutritive juices are dispersed through the system. This consists 

 of a delicate network of vessels, arising from three large trunks, 

 one placed in the centre of the dorsal aspect, and the other two 

 running along the sides of the animal (Jig. 39, 2). 



(120.) The Planarise are perfectly androgenous, as each indi- 

 vidual possesses a distinct male and female generative system ; but 

 they are not apparently self-impregnating, as the co-operation of two 

 individuals has been found needful for the mutual fertilization of 

 their ova. In every one of these animals two distinct apertures 

 are seen to exist upon the ventral surface, at a little distance be- 

 hind the root of the proboscis ; the anterior of which gives issue to 

 the male organ, while the posterior leads to the oviferous or fe- 

 male parts. 



In Planaria tremellaris, the penis, which during copulation is 

 protruded from the anterior orifice, (Jig. 89,* 6,) is a white, con- 

 tractile body, enclosed, when in a retracted state, in a small oval 

 pouch; it is perforated by a minute canal, and receives near its root 

 two flexuous tubes, which gradually decrease in size as they diverge 

 from each other, until they can no longer be traced. These are 

 the seminiferous vessels (Jig. 39, 5, a). The posterior genital 

 orifice, which leads to the female organs, communicates with a small 

 pouch, or uterus, as it might be termed (Jig. 39, 5, b) : into this 

 open two lateral oviducts, which run on each side of the male ap- 

 paratus and of the proboscis ; these are very transparent, and only 

 recognisable under certain circumstances by the ova which they 

 contain. In Planaria lactea the oviduct opens into the uterine 

 cavity by a single tube, which, passing backwards, divides into two 

 equal branches ; and both of these, again subdividing, ramify 

 extensively among the cseca derived from the stomach. We 

 likewise find in this species two accessory vesicles, which pour 

 their secretions into the terminal sac. 



(121.) The Diplozoon paradoxum is another form, which, 

 though it cannot strictly speaking be classed with the entozoa, is 

 so nearly allied to Distoma in its internal structure, that its 

 anatomy will be most conveniently examined in this place.']" 



This remarkable animal, as its name imports, is literally pos- 

 sessed of two bodies, precisely resembling each other in every 

 particular, and united by a narrow communicating band, so as to 

 form but one animal, the nutrient canals of one division commu- 



* This figure represents two Planariae as they appear in the act of sexual inter- 

 course, t Nordmann. 



