106 A. P. THOMAS. 



unable to assist me. The comparative freedom from rot of 

 sheep in the neighbourhood of Oxford last year was probably 

 due to the real scarcity of this snail. 



In 1882, however, there were floods in July, and the waters 

 of the Isis brought down vast multitudes, probably from its 

 breeding haunts in marshy places up the river. So numerous 

 was it, that a single sweep of a small hand-net repeatedly 

 gave me more than 500 examples, and this was in a ditch 

 where last year not a single L. truncatulus could be found. 



On obtaining the snails I had so long been searching for, I 

 exposed a number to infection by placing fluke embryos in 

 the vessel with them. The snails were speedily found to have 

 afforded a suitable place for the further development of the 

 embryos ; indeed, infection was too successful, for very large 

 numbers of them died simply from exhaustion owing to the 

 excessive number of parasites they contained. 



It may be well to mention here that infection experiments 

 have been tried upon the following species of molluscs, as well 

 as uponL. truncatulus, viz., Limnseus pereger, L. palus- 

 tris, L. auricularius, L. stagnalis, Physa fontinalis, 

 Planorbis marginatus, P. carinatus, P. vortex, P. 

 spirorbis, Bythinia tentaculata, Paludina vivipara, 

 Succinea amphibia, Li max agrestis, L. cinereus, Arion 

 ater, A. hortensis. None of these could be infected, with 

 the partial exception of Limnseus pereger. With regard 

 to this last species I can corroborate Professor Leuckart's 

 statement that the youngest specimens only of this species can 

 be infected, and that even here development does not proceed 

 beyond an early stage. 



Although it appears that L. truncatulus is the only Eng- 

 lish mollusc which can serve as intermediate host to the liver- 

 fluke, it is quite possible that elsewhere some other mollusc of 

 similar habits may be victimised. L. truncatulus has a very 

 wide geographical distribution, but so, too, has the liver-fluke; 

 and if the latter has the wider distribution, there must of course 

 be some other intermediate host. Leuckart^ states that 

 ' ' Die menschliclieu Parasitcu,' p. 531. 



