see page 280. 



Fig. 288. Qculotrema hippopotami 



Stiinkard, adult worm. Magnified 



20 times. (According to Stiindard, 

 1924). 



Polystoma- 



The basic tendencies of 

 the development of the family are 

 obvious. Thus, we see a gradual 

 complication of the digestive system 

 from the simple 2-branched intestine, 

 with trunks not merging at the end 

 (Polystomoides and others) and then 

 the gradual appearance of outgrowths 

 on the trunks ( Protopoly stoma ), 

 later the merging of the trunk at the 

 posterior end (Diplorchis) and finally 

 the appearance of interior outgrowths 

 and anastomoses ( Polystoma) . At 

 the same time, the process of compli- 

 cation of the sex system takes place. 

 Among simply organized genera there 

 is only one testis and there is no 

 uterus in the real sense of the word; 

 it is functionally replaced by an ootype 

 containing one egg (Polystomoides and 

 others). Further development pro- 

 ceeds along the lines of an increase 

 in testes (Diplorchis --2 testes. 



p. 401 



-follicular and numerous) and the elongation of the uterus 

 (Parapolystoma, Diplorchis and Polystoma ). The functional significance 

 of these changes has already been noticed (see page 128). The processes 

 of the progressive changes in the structure of the separate systems of 

 organs do not coincide with each other and among Parapolystoma , for 

 instance, we see only one testis but a very long uterus, with the presence 

 of a more simply organized intestine. It is interesting to note that 

 Oculotrema, parasitizing the eyes of the Hippopotamus (see however, page 

 219 ), has a rather primitive structure of the digestive and sex systems 

 while it has a very powerful development of the attaching disc (Fig. 288). 

 As regards the "primitiveness" of the sex system, this apparently is a 

 secondary phenomenon, because in this genus the armature of the copulatory 

 organs and the vaginal ducts are absent. These cannot be considered in this 

 case as characteristics peculiar to ancestral forms. 



2. Family Sphyranuridae Poche, 1925 

 (Figs. 35, 101, H, 216-219) 



480 



