45. 



being ta>n_. r ^t a sin/-"!, e .ne-il 11 * That the American 

 ducV, Marl la nrvrila (Linn.) ^ts anails is certain 

 the oxaflt pel has, so far as I Vncw, never b<*f?n 



tabulated. The mallard dud's eat over 90 per" cent 



table food in the wild, but it is lively that a ft till 

 rg^r ;j-r cent ig of vendible matter in parl r ft where they 

 e -.Vuly fed* 5br this reason I should expect to find 



living on ponds Cher's additional food i not supplied an 

 where th< eoiiinootoae infection cf snails is squally heavy, 

 to be <aore par^9iU2*d with the eh ina 8 tom g,dtiltB than those 

 faed in a pat^* *iho s*oond *ay is that of duad snails 

 ten by dud^-s, f5e0se, toi ihuidr^cUt nf apeoimens of 

 were se<tn dAd on the surface of Stow 



Binoe this water is not used for Drinking purposes, and 

 thus no ohenioals are used, and beoau^e there were also 

 healthy active snails, I feel sure that their death was 

 caused largely by the eohiooetome p-ivasiteB* 'ili^ dread 

 snails wre found upon examination to be heavily parasitized 

 in nearly every oase. Sometimes the infection i so heavy 

 that in quantity it is about one-third the size of the viscera 

 of the snail* If only cysts were present, I should say little 

 h'-rm -Mould b'ji&one but with an abundance of rediae also 

 absorbing food and {giving off wastes into the body, oon- 

 8ider->.ble injury is bound to be done ana in extreme oases 

 I believe death results. Labour (1912, p* 423) snys this 

 oonoernin^i the effeat of tJi> parasite on the host* w The 

 presence rf ?porooyats and rediae aertainly injures the 

 mollusoan host* The outer appearance of the digestive gland 

 la usually enough to show if it is inhabited by these 

 parasites* It looJra unhealthy and is a grey, siokly yellow 



