DISTOMA HEPATICUM. 251 



two main stems above mentioned. Besides these, on tlie space 

 between the month and the base of the ventral sucker, there are 

 on each side five very short, slightly branched stems, which run 

 forwards and laterally. This structure of the intestine is an 

 essential point to furnish us with data in any inquiry after the 

 young of this Distoma dispersed amongst the lower animals. We 

 may expect, a priori, that amongst the cercariform creatures, those 

 alone can belong to D. hepaticum which exhibit a similar ar- 

 rangement of the intestinal canal. By continued pressure from 

 behind forwards, the entire contents of the intestine may be 

 expelled. The intestine is soon freed spontaneously by long 

 keeping of the animal in water or bile. Sometimes, also, we find, 

 the larger Distoma, when wedged into the narrow ducts of the 

 liver, deprived of their biliary contents. As regards the position 

 of the intestine, I think that we shall come nearest to the truth 

 if we place it about the middle of the parenchyma, and neither 

 nearer to the dorsal nor to the ventral surface. 



Excretory organ. — Under this denomination we combine, what 

 particular authors have treated separately under the names of 

 respiratory and circulatory systems and excretory organ, or 

 aquiferous system and excretory organ. But in the first place 

 there is no respiratory system, either in the Trematoda in general, 

 or in our Distomum in particular. Neither can we speak, either 

 of distinct circulatory and excretory organs, or of a separate 

 aquiferous system and excretory organ. Both are only parts of 

 one and the same svstem. It is to Van Beneden that we owe 



it 



the first discovery that the aquiferous system passes into the ex- 

 cretory organ, and where this takes place. Aubert has recently 

 confirmed Van Beneden's observations as regards Distoma iere- 

 ticolli, and has positively seen one of the granules of the aquiferous 

 system, of which we shall speak presently, slip into the excretory 

 organ and return again from this into the aquiferous system. 

 This transition is also certain in Nordmann's Diplostoma, and in 

 the Diplost. rachicsum of Henle, so that Aubert thinks that we are 

 perfectly justified in applying these observations, per analogiam, 

 also to the other Trematoda, and regarding the whole of the 

 organs here treated of as one and the same ; namely, as an 

 excretory organ. 1 For the investigation of the structure of this 



1 In Von Siebold and Kollikei's ' Zeitschrift,' vi, pi. xiv, fig. 3 A, the passage of the 

 so-called water-vascular system into the excretory organ is very beautifully represented 



