DECREASE OF ANIMAL LIFE 373 



creatures which fed upon them, such as the marsh-fre- 

 quenting birds, and the Otter, still a characteristic in- 

 habitant of the Norfolk "Broads." 



To take first a few actual examples of the effects upon 

 denizens : The remains of hundreds of Common Frogs and 

 Toads, and those possibly of the Natterjack Toad, now 

 unknown north of the Scottish shores of the Solway Firth, 

 have been found in deposits of the Neolithic period, in the 

 Bone Cave of Allt nan Uamh in western Sutherland, where 

 no marsh has existed for long ages and where now even the 

 burn itself runs underground. It is true that, in the locality 

 mentioned, nature and not man has been the reclaiming agent, 

 but this does not affect the example as typifying one obvious 

 result of disappearing marshes the disappearance of crea- 

 tures vitally associated with them. 



The vanishing of two of the humbler inhabitants of the 

 swamps is also worth recording, on account of their special 

 interest to man. With the marshes and wet places perished 

 the main breeding-places of the Mosquito, the larvae of 

 which live in shallow pools; and since the Mosquito conveys 

 to man the germ of malaria or ague, with the Mosquito dis- 

 appeared that dreaded disease, which was once far more 

 common in Scotland and England than it is at present (see 

 p. 508). In the same way, the draining of the fields has 

 ruined the home of a Pond Snail (Limn&a trnncatula}, 

 the host in which one stage of the Liver-fluke (Fasciola 

 hepatica] develops. But a single break in its life-history 

 extirpates the Liver-fluke, and the ultimate result of the 

 disappearance of the Pond Snail has been that from many 

 districts liver-rot in sheep, which was caused by the adult 

 Liver-flukes, has been entirely banished; so that reclamation 

 has all but removed a fatal disease which formerly caused a 

 loss of sheep in the United Kingdom estimated at a million 

 a year. 



Nor must we forget that the numbers of microscopically 

 small inhabitants have been even more seriously reduced, for 

 some of these are particularly sensitive to alterations in 

 physical conditions. In the summer of 1897, Dr Thomas 

 Scott found an artificial pond in the neighbourhood of Edin- 

 burgh swarming with the Water- flea, Daphnia pulex. Seven 

 weeks later, as the result of a spell of dry weather, the pond 



