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No. 41. 



THE HABITATS OF LIMNAEA TBUNCATULA AND L. PEREGEB IN 

 RELATION TO HYROGEN ION CONCENTRATION. 



By W. R. G. ATKINS, O.B.E., P.I.C, 



AND 



MARIE V. LEBOUR, D.Sc, 

 Marine Biological Laboratory, Plymouth. 



(Bead January 29. Printed February 22, 1924.) 



L. truncatula lias long been the accepted intermediate host of the liver 

 fluke Fasciola hepatica, and it has recently been pointed out by Taylor (1922) 

 that sheep are infected with liver fluke in parts of Scotland from which 

 L. truncatula is absent. L. pereger is, however, found there, and has been 

 proved to be infected with the cercariae of F. hepatica. The authors (1923) 

 liave already shown that the distribution of many snails is limited by acidity, 

 whereas others are found in acid or almost neutral, but never in alkaline 

 habitats. Attention was drawn by Wallace (1922) to the opinion of Welsh 

 farmers that liver fluke was mox^e prevalent on land which had been limed 

 than on untreated pastures. Since the sheep pastures of Wales are notoriously 

 poor in calcium carbonate the liming must produce a considerable change 

 in the soil reaction, but the reaction is unlikely to be at all as alkaline as 

 in limestone or chalk districts. There appeared, therefore, to be indications 

 that an almost neutral reaction favoured L. truncatula. In view of the fact that 

 in certain wet years the ravages of liver fluke among sheep become disastrous, 

 it appeared to be of interest to ascertain what characteristics might be used 

 to define localities in which L. truncatula or L. pereger could develop or 

 could abound. This appears to be the more desirable, inasmuch as it is often 

 the custom to bring sheep down from hill pastures free from these snails 

 to winter in lowlands, which are normally less acid than the hills. The work 

 of Walton (1923), on the destruction of L. truncatula by means of copper' 

 sulphate, has, however, demonstrated that habitats naturally veiy favourable 

 may be almost or entirely cleared of this snail. 



L. truncatula probably attains its greatest abundance in water-logged 

 pastures. Boycott (1919) does not consider it as a water-snail, though it 

 occurs in three "drying" ponds out of a total of one hundred and forty-one 

 "closed" ponds in the parish of Aldenham. It is nowhere recorded by him 

 among the sixty-nine land mollusca of Aldenham and its district (1921). 

 This district, therefore, is apparently not a favourable habitat for L. truncatula ; 

 L. pereger, on the other hand, is truly a water-snail. Boycott (1919) records 

 its occurrence in fifty-one out of one hundred and eight ponds examined by 

 him, as well as in lakes and streams, though not in any of the seventeen 

 "drying" ponds. Stelfox (1911) records the general occurrence of L. pereger 

 in the Clare Island survey, and remarks upon the swarms of a small fonn 



SCIENT. PKOC. E.D.?., VOL. XVII, KG, 41. 3q 



