LIFE HISTORY OF THE LIVER-FLUKE. 131 



a path near the ditch, and these seemed to have crawled out 

 of the grass when revived by the rain. At the roots of the 

 grass, along the margin of the ditch, others were found in 

 abundance. Some few shells were quite empty, but the ma- 

 jority contained the dried remains of the snail, which had 

 shrunk far back into the spire of the shell. Most of these 

 appeared to be quite dead, but were, however, merely dormant, 

 for on placing them in water the tissues imbibed moisture 

 and assumed their normal bulk, and after a few hours the 

 snails had regained their full activity, and were seemingly none 

 the worse for their prolonged desiccation. To test their power 

 of resisting drought I collected specimens of L. truncatulus 

 and placed them in an open vessel on a shelf in a dry labora- 

 tory, in a position where the sunshine fell on them for an hour 

 or so daily. I found that rather more than 50 per cent, with- 

 stood twenty-six days of this treatment, and some few revived 

 after more than six weeks. That the snails can live on moist 

 ground quite away from any quantity of water for considerable 

 periods, is sufficiently proved by the fact that I have kept them 

 alive for eleven weeks on moist grass and moss, even when 

 infested with Fasciola hepatica.^ 



It is clear, therefore, that the species of snail under con- 

 sideration, when left on the fields by the passing away of a 

 flood, continues to wander and feed so long as the bottom of 

 the grass remains moist. It is equally clear that the numbers 

 so left are recruited from surrounding ditches and streams. A 

 drought may render the snail dormant, but, unless too long 

 continued, it revives at the first shower of rain. If there 

 are fluke-eggs on the ground and water in puddles or ditches 

 for them to develop in, the L. truncatulus will most certainly 



' Sir Charles Lyell ('Life,' vol. ii, p. 212), in speaking of Madeira, says 

 that Limnaeus truncatulus was unintentionally introduced by the Por- 

 tuguese thirty years before, and has spread so widely that it is now found even 

 in the pools and ruts in the roads, so that it must have a mode of distribution 

 which needs investigation. It will be seen from the above account that the 

 terrestrial habits of this snail, and its power of withstanding drought, are 

 amply sufficient to explain its spread in Madeira. 



