38 Bepori of the Bilharzia Mission in Egypt, 19] 5 



stage shows no sexual differentiation, consequently the absence of 

 pharynx in the cercaria (fig. 19) is the one reliable character upon 

 which a bilharzia cercaria can be distinguished from the cercarise from 

 other distomes, because the body of the cercaria without further 

 metamorphosis grows to become the body of the adult worm. 

 All cercaria have a motile tail at the posterior end. This 

 appendage is a purely larval structure both morphologically and 

 functionally. It serves the definite object of enabling the cercaria 

 body to travel from the intermediate host to some favourable 

 position where it can gain entrance to the final host. The tail is 

 always shed before the actual arrival of the cercaria in the tissues 

 of its host. Various cercaria exhibit different types of caudal 

 appendage. In the four bilharzia cercaria that have come under 

 the notice of the writer the tail was forked at its free end. This 

 peculiarity, however, is shared with some other widely different 

 forms among the distomes. It will be shown in the latter part of 

 this report that four distinct sub-groups of bifid-tailed cercaria 

 occur in the mollusca of Egypt. 



Attraction of Mollusca for Bilharzia Miracidia. 



Looss states that none of the Egyptian mollusca exhibited the 

 slightest attraction for the freshly hatched miracidia of bilharzia. 

 Most of the species submitted to experiment by us were entirely 

 ignored by the miracidia. A definite attraction, however, was 

 exhibited by the following : Planorhis hoissyi, Bidliniis sp. {?), 

 Pyrgophysa forsl-ali, 3ind LinincBa truncatula. The attraction was 

 stronger in young specimens. This plurahty of susceptible forms 

 appeared to indicate the possibility of a plurality of intermediate 

 hosts or the susceptibility of the Bilharzia hamatohia miracidia to 

 the intermediate hosts of other species of bilharzia, or merely, as 

 seemed probable in Limnaa truncatula, to a peculiar adhesiveness 

 of the mucus covering the exposed portion of the mollusc body. 



It may be noted here that not a single specimen of Linmcea 

 truncatula could be found in or around Marg. 



Marg Molluscs found infected with Bilharzia. 



Large numbers of snails collected from the Marg Canal through- 

 out its course, but more especially within the village, were infected 

 with larval forms showing the morphological peculiarities of the 

 bilharzia group. The infected shells were readily obtained at spots 

 daily frequented, such as the praying ground at the embankment 



