469] LARVAL TREMATODES — CORT 23 



The digestive system in Cercaria diastropha is similar to that of 

 Cercaria inhabilis, but the oral sucker and its pouches are larger in 

 proportion to the size of the acetabulum, and the intestinal ceca reach 

 nearer the posterior end of the body. 



In Cercaria, diastropha the anlage of the reproductive organs is 

 further developed than in Cercaria inhabilis. It is differentiated into 

 four clearly separated areas, which bear the same general relation to 

 the adult organs as in the other species. They are not however con- 

 nected with strands of nuclei and are not in exactly the same relative 

 position as in Cercaria inhabilis. 



The above descriptions show that Cercaria inhabilis and Cercaria 

 diastropha differ considerably in the size and shape of the body, the ratio 

 in size of the suckers and in the position of the acetabulum, the amount 

 of pigmentation, and in the anlage of the reproductive organs. 



Rediae of Cercaria diastropha (Fig. 25) were in different stages 

 of development. No rediae were found in which other rediae were 

 developing and in none were the cercariae further dveloped than in the 

 rediae of Cercaria inhabilis. The rediae were very mobile, having remark- 

 able power of changing their shape, and with the aid of the posterior 

 locomotor appendages could move fairly well. In the younger rediae 

 the body would sometimes be extended to five or six times the length 

 when contracted. This mobility is correlated with the extereme devel- 

 opment of the circular muscles, which show clearly as annular bands 

 (Fig. 25, ab). In the young living redia part of the excretory system 

 could be made out. One longitudinal trunk from the anterior extremity 

 was traced until it met two trunks from the posterior end. 



In the youngest redia studied there were practically no germ 

 balls in the body cavity; the length of a toto mount slightly contracted 

 was 0.45 mm. and the greatest width 0.13 mm. The intestine extended 

 to a point 0.22 mm. from the anterior end and was relatively voluminous. 

 The oral sucker had a length of 0.43 mm. and a width of 0.032 mm. 

 One of the largest specimens measured 0.78 mm. in length and 0.16 

 mm. in width. The intestine reached one-third the body length. The 

 oral sucker was about the same size as in the younger specimens, the 

 length being 0.044 mm. and the width 0.038 mm. From the above 

 description it is evident that the redia of Cercaria diastropha is very 

 much like that of Cercaria inhabilis. The greatest difference is in a 

 greater mobility correlated with a greater development of the circular 

 muscles in the former. 



Altho a large number of adult trematodes belonging to the family 

 Paramphistomidae has been described, I have found in the literature 



