130 A. p. THOMAS. 



minutes a layer of considerable thickness is formed, whilst its 

 substance begins to harden. The cysts, as already remarked, 

 are snowy-white, but the body of the included Fasciola is 

 quite transparent. 



The habits of the intermediate host (Limnseus trunca- 

 tulus) are of much importance, as showing the manner in 

 which the cysts are distributed in places where they are likely 

 to be picked up by some herbivorous mammal, within which 

 they can attain the adult state. Liranseus truncatulus 

 belongs to the group of fresh-water Pulmonata ; it is a common 

 snail, but one which is often very difficult to find on account 

 of its small size and peculiar habits. It has a very wide 

 geographical distribution, being found, according to Dr. Gwyn 

 Jeffreys, throughout Europe, in North Asia, Morocco, Algeria, 

 Madeira, and (doubtfully) in Guatemala. Several species be- 

 longing to the genus Limnseus occasionally crawl for short 

 distances out of the water, but in L. truncatulus this habit 

 is so much more strongly developed that the snail should be 

 termed amphibious. Indeed, it is oftener found out of the 

 water than in it. When kept in an aquarium it quits the 

 water, and as often as it is put back crawls forth again so long 

 as the necessary strength remains. It is said to breed on 

 the mud at the sides of ditches. To show how much it lives 

 out of the water I may briefly relate ray own experience. 

 There were floods on the Isis in July last, and the waters 

 brought it down in vast multitudes, probably from its breeding 

 haunts in marshy places far up the river. It was extremely 

 abundant, and a single sweep of a small hand-net repeatedly 

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

 previously I could not obtain a single L, truncatulus. 



All along the margins of the ditches the ground was covered 

 by them, and they were found in numbers on the flooded ground 

 when the flood waters had retired. On returning a month 

 later to the same ditches I was unable to find a single example 

 alive in the water. There had been dry weather since the flood, 

 but early that morning heavy rain had fallen, and I found 

 numbers of specimens of L. truncatulus out on the gravel of 



