C. L. Walton 
243 
the jaw is locally considered the chief external sign of the disease 
though some of the more experienced men recognise that a sheep may 
show this symptom and yet recover, or may be attacked and not show 
it at all. It is, however, generally regarded as denoting a severe case, 
though I have seen an ewe that showed this symptom in February 
and yet reared her lamb successfully. A number of ewes will pull 
through until lambing time and then die, as I have myself witnessed. 
The usual local treatment for rot, consists of slitting open this “bag” 
with a knife and then rubbing in salt. This may be done several 
times and is claimed as a cure, and instances are cited where sheep have 
recovered after the treatment; from what has been said it will be 
evident that recovery might result without the operation. One ewe 
is stated to have been “cut” three times and later reared three lambs 
ere being sent to the butcher three years later, her liver was then found 
to be “like a stone.” Occasionally a seton is put in the “bag.” 
III. Observations on the Bionomics op Limnaea truncatula'. 
The Distribution of L. truncatula and L. peregra. 
Upon receiving instructions to study the Liver Rot-of Sheep and the 
Bionomics of L. truncatula within the Aberystwyth Area, in the autumn 
of 1913, my first endeavour was to discover as far as possible the 
distribution of the disease through the Area, and at the same time to 
trace the occurrence of the host snail. I speedily discovered that two 
species of the genus Limnaea were abundant in the Area: L. truncatula 
and L. peregra. One solitary specimen of L. palustris was found in 
Feb. 1916, in a streamlet at the head of the Teifi. watershed on the 
extreme southern margin of the area examined. 
It also became apparent that L. truncatula and L. peregra showed 
a marked difference in habitat. Although frequently found in the same 
stream or ditch, their distribution is but rarely found to coincide, and 
when this does occur, it is in the nature of an overlap, one species or 
other predominating. 
The bionomics of L. peregra were followed to some extent also in 
order better to understand L. truncatula. In general the life histories 
and distribution are similar; in detail they differ. The main physical 
features of the Survey Area have already been outlined ; it will therefore 
suffice to say that the chief factor governing the distribution of the 
species is the distribution of clay; in this Area frequently of glacial 
