646 THE ANIMAL KINGDOM. 



Ciliated funnels have been detected in several monogenetic Tre- 

 matoda, e. g. Polystomnm integerrimum. There is generally a system of 

 canals corresponding to the two sides of the body which branch and 

 anastomose. In Aspidogaster and Stichocotyle there is a posterior terminal 

 pore, from which two contractile (?) vessels originate. But in Tristomum, 

 Psetidocotyle, Epibdella, &c., each main lateral canal terminates in a small 

 vesicle, and the two vesicles open on the ventral aspect of the body 

 anteriorly, one on either side of the pharynx. The two apertures are said 

 to be dorsal in Polystomum integerrimum and Axine, but in Onchocotyle 

 they are posterior, and situated respectively at the ends of the two 

 contractile processes of the body. In most Polystomeae the excretory 

 system is imperfectly known 1 . 



The Trematoda are hermaphrodite with the exception of Bilharzia 2 . 

 The male organs consist of the testes and efferent canals. The former 

 usually lie near the centre of the body, and just behind the ovary. There 

 is but one testis in Udonella Caligorum, Octobothrium lanceolatum and 

 Calceostoma elegans. In other instances there are two, one somewhat in 

 front of the other. They are generally more or less globular, sometimes 

 lobed. In most of the monogenetic Trematoda the lobes are well marked, 

 and the testes are frequently broken up into independent follicles, e. g. 

 Tristomum, Polystomum. The digenetic genus Fasciola alone has branched 

 tubular testes. The vas deferens is formed by the union of two or more 

 efferent vessels according to the number of testes or testicular follicles. 

 It is dilated more or less, for the first part of its course forming a vesicula 

 seminalis ; and in some Distomidae the part of the canal following the 

 vesicula has cellular walls, and is surrounded by a number of unicellular 

 glands which open into it, thus constituting a prostatic region. Similar 

 unicellular glands are present in some monogenetic Trematoda, e. g. 

 Polystomum. The terminal portion of the canal is generally more or less 

 evaginable, and is surrounded by a muscular cirrus-sac, sometimes absent, 

 e. g. D. clavatwn, which may in some Distomidae include only the prostatic 

 region, or the vesicula seminalis also, together with the terminal portion. 

 The sac appears to be composed of external longitudinal and internal 

 circular muscular fibres. Among monogenetic Trematoda the genera 

 Calicotyle and Pseudocotyle have the vas deferens terminating in a per- 

 forated chitinoid piece : while Axine, Microcotyle, Polystomum^ Gyro- 

 dactylus, &c., have a circlet of hooks (?) surrounding its aperture. The 

 female organs consist of a germarium, vitellarium, their ducts, a shell- 

 gland, and oviduct. The germarium is always single, usually globular or 

 elongate, and even folded on itself, e. g. Octobothrium, sometimes lobed, 



1 Calcareous bodies are stated by Cunningham to occur in the two main canals of Stichocolyle. 



2 It is possible that D. filicolle ( = Kollikeria of Cobbold, D. Okeni of Kolliker) is another 

 example. See P. J. van Beneden, C. R. Suppl. ii. 1861, p. 186. 



