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Records of the Indian Museum. [Vol. XXII, 



cercaria and Ecliinostome cysts at the end of the ist year of life, 

 whereas at the end of the second year there is no such distinction 

 between the two sexes. In cases where infection is heavy the 

 auricle is so packed with cysts that it is a matter for wonder 

 that it is able to perform its function at all, and in the case of the 

 gills their physiological activity must be very seriously interfered 

 with, leading to impaired vitality and a lowered resistance to 

 adverse conditions. It is not improbable that we have here, if 

 not the sole explanation, at least a contributory cause towards the 

 marked progressive reduction in the proportionate numbers of adult 

 males during the period of life succeeding the attainment of sexual 

 maturity that, as we have already seen, occurs in this species. 



Table 3. — Showing the degree of infection present in adult ex- 

 amples aged one and two years. 



The occurrence of Ecliinostome cysts in the auricle is by no 

 means restricted to Vivipara bengalcnsis, nor is it confined to any 

 particular district or country. Filippi {1855, p.. 345) has recorded 

 the occurrence of similar Echinostome cysts in the auricle of Vivi- 

 para vivipara, and he has further noted "qu'il ne m'a jamais ete 

 possible de voir la moindre trace de ces parasites dans les foetus 

 des Paludines ; mais que les jeunes individus, pourvu qu'ils aient 

 vecu quelques mois en liberte dans I'eau du lac en sont deja 

 enrahis." His results obtained in Europe agree, therefore, 

 closely with the observations made in India. The occurrence of 

 these cysts has also been noted by Moulinie (1886, p. 193). 



As regards the geographical distribution in India, I have 

 found these cysts present in examples of V . bcngalensis, taken 

 from five different areas of water in the Calcutta district. It is 

 worth noting, however, that in examples of the phase annan- 

 dalei^ taken from a tank in Baliaghatta, this infection was absent 

 in ten specimens that I examined : other examples from the same 

 source were placed in experimental tanks, and when thej- were 

 examined about 2 months later in every case cysts were present, so 

 that infection had occurred during their sojourn in the experinren- 

 tal tanks. Extrem.ely similar, if not absolutely identical cysts 

 were found in identically the same situation, namely the auricle, 



