20 BNTOZOA. 



Genera. — Monostoma, Zeder ; Nematobothrivm, Van Beneden. 



Distomidce. — This family embraces the principal and best 

 known genera of the order, and its members are at once recognized 

 by the presence of two pores or suckers ; one, the anterior, being 

 connected with the mouth, the other, or the so-called acetabulwn, 

 being usually placed on the ventral surface, in the middle line. In 

 some cases, as in AmpMstoma, the acetabulum is situated at the 

 posterior end of the body. In the arrangement of Yan Beneden, 

 the Distomes represent his digenetic section of the Trematoda, 

 because in them (and in Monostomidse) we have a double method 

 of propagation — in other words, an alternation of generation — by 

 eggs in the first instance, and by internal budding (agamogenesis) 

 afterwards. 



General structure. — It is a frequent habit with naturahsts to 

 select the common hver fluke (Fasciola hepatica) as a type of this 

 family ; but as this species deviates very markedly from aU the other 

 genera included in the family, and in respect of its digestive system 

 approximates very closely to the Planaridae, I purposely select some 

 more simple and less known form to illustrate the general anatomy 

 of the family under consideration ; at the same time reserving the 

 common fluke for minuter anatomical details in the second part of 

 this work. 



The small fluke here selected is the Distoma conjunctum, 

 numerous examples of which I discovered (1858) in the liver 

 of the American red fox {Ganis fulvus). A group of them are 

 represented of the natural size (plate ii. fig. 1). Tig. 2 is an 

 enlarged view of one of these parasites, showing its pyriform outline 

 and smooth integumentary surface (x 35 diam.). At the anterior 

 extremity is a round oral sucker (a), the acetahulum being placed 

 at the lower part of the upper third division of the body (b). 

 The mouth, properly so called, is placed at the base of the cephalic 

 sucker, and leads into a small, oval, muscular oesophageal bulb (c), 

 the latter directly communicating with two long, cylindrical, diges- 

 tive canals {d, d) ; these widen out a little as they approach 



