288 Records of the Indian Museum. [Vol. XXII, 



Parasites and Incolae. 



Amongst the normal inhabitants of the alimentary canal of 

 Vivipara bengalensis and probably of other species of the same 

 genus are several different types of ciliate protozoa, and it seems 

 worth putting on record that in almost every individual examined. 

 I have found what appear to be Spirochaetes in both stomach 

 and intestine. There appear to be two different forms. One of 

 these measured o"026-0028 mm. in length and shows 6-7 curves 

 in the spiral ; it is highly refractile and quite easily seen under a 

 high power. It moves backwards or forwards with equal facilitj'. 

 At times individuals are met with which show a narrow thin 

 portion in the middle of their length, while short individuals having 

 a length of o'oi4mm. and only 3 curves in the spiral are occasion- 

 ally met with. It appears that these short forms are produced by 

 transverse fission of the larger individuals. The second form of 

 Spirochaete occurs in the rectum and measures o'oi4-o-oi6 mm. in 

 length ; it is of a robust type and has two or three wave like bends 

 in the course of its length. 



In addition to the above, there is a rich bacterial flora, 

 consisting of diplococci, rod-hke bacilli, etc., in both stomach and 

 intestine. 



Vivipara bengalensis rarety acts as the primary mollusc host 

 for the development of Trematodes. In this respect it forms a 

 marked contrast to other species of the same genus, for Vivipara 

 fasciata Miill. has been recorded as the primary host of nine 

 different cercariae, and V. vivipara (L.) harbours as many as eleven. 

 Out of a total of 283 examples of V. bengalensis I have onlj- 

 succeeded in finding cercariae on two occasions and in both indi- 

 viduals it was the same form that was present. This cercaria 

 belongs to the group of Xiphidiocercariae, and was developing in 

 small oval sporocysts.' In both cases the host was a male and 

 development was taking place in the testis. 



On the other hand, it is often extremely difficult to find an 

 example that is not acting as an intermediate host. Two kinds of 

 Agamodistome.s'^ infect and become encysted in this species and 

 each has a very distinct anatomical distribution. One tj^pe of cj'st, 

 which is circular in shape, is found in the auricle of the heart. 

 These cysts enclose a stage in the development of an Echinostome. 

 The other cyst is found in the gill-bars, it is oval in shape, and 

 usually of a pale brown colour and enclosed within it is a small 

 Agamodistome, that judging from its structure is derived from a 

 Xiphidiocercaria. I am unable to say whether this Agamodistome 

 represents a further phase of the life-history of the cercaria noted 

 above, but the two are extremely closely related and both possess 



' For a description of this Cercaria see Sevvell, " Cercariae Indicae," Jtidian 

 Journal of Medical Research (in the press). 



2 Dollfus(M«m. Soc. Zool. France X.X\' , p. 87, Paris, 1912) has introduced 

 the term ' Metacercaria ' to describe the stage in the life-history of a Trematode 

 hetvveen the free-living cercaria and its final establishment in its definitive host. 



