250 ANIMAL PARASITES. 



These structures resemble the squares (Felder) in the foot or in 

 the sucking cup of Aspidog aster conchicola, figured by Aubert, 

 I cannot help thinking that the structures seen by me are the 

 same which have led Keber and others to speak of pores in other 

 Trematoda. I regard the squares or spaces in question as 

 vacuoles, which become inflated and filled with water by con- 

 tact with that fluid, but are not so easily perceived when the 

 animals are treated without water. They appear and disappear, 

 therefore, according as the interior of this obtuse muscular cone 

 is full or empty of fluid, according as its inner walls are in con- 

 tact or kept asunder. 



Nervous system and organs of the senses are wanting. 



Alimentary apparatus, This apparatus is composed of a mouth 

 placed at the anterior point of the body, that is the so-called 

 anterior sucker. This is followed by a sort of constriction 

 (oesophagus), and this by a goblet-shaped pharynx, the larger 

 opening of which is directed forwards, but backwards when 

 broken. The pharynx consists of two layers of contractile sub- 

 stance. According to Aubert, in Aspidogaster the inner layer is 

 longitudinally and the outer transversely striated, without its being 

 a true transversely striated muscular substance. The case is 

 exactly the same in D. hepaticum. It is only to be observed, 

 that the anterior margin of the pharynx appears as if notched. 

 For this reason it may be thought to be composed of several 

 pieces ; I always believed that I could count three such segments. 

 The pharynx is followed by a very short, simple, somewhat nar- 

 rowed portion of intestine, which runs to the level of the sac of 

 the penis, where it divides into two large stems, which, making 

 a small excursion, run round on the sides of the sac and 

 ventral sucker, and again approach each other behind the ventral 

 sucker, without, however, uniting by anastomoses, and finally 

 run parallel and near to each other to the hinder margin of the 

 Distomum, where they terminate in caeca. This intestine is dis- 

 tinguished from that of many other Distoma, in that a quantity 

 of variously dendritic branches are given off laterally from the two 

 main stems, the finest ramifications of which run to the lateral 

 margins of the animal, where they terminate in cseca without anas- 

 tomosing. All these branches of the intestinal canal contain bile 

 in our Distomum, and by this means, when they are full, their 

 course may be very clearly traced. In large Distoma I have 

 counted 14 15 lateral branches on each side, given off from the 



