ARION ATER. 173 



is believed to be impregnated with its matter, the shig is then securely 

 impaled upon a thorn, where it dies, and gradually withers up, by which 

 time the wart will also have disappeared. In Northamptonshire it is con- 

 sidered necessary to repeat the operation on nine successive nights, by 

 which time the wart will have gone. 



In 1890 Mr. Kew observed an old man in a garden at Highgate, in the 

 suburbs of London, engaged in gathering A. ater for the purpose of making 

 ointment ; while in Lincolnshire the appearance of "black snails" is regarded, 

 especially at harvest time, as a most reliable sign of impending rain. 



In former times, the ancients in their ignorance of moUusca, believed 

 that slugs in general, and this one in particular, as being the most obvious 

 and conspicuous of them, to be the same animals as those possessed of 

 shells, and Albertus Magnus and Gesner, influenced in part by a passage 

 in ^lian, believed that snails had the power of quitting and returning to 

 their shells at pleasure, while Kramer in 1736 attempted to prove that 

 this was actually the fact. 



Fossil. — The chalky granules, believed to be the internal shells of 

 A. ater, are recorded by Sandberger from the gravels and brick -earths of 

 the Upper Pleistocene beds of this country. 



Pleistocene. — Messrs. Kennard and Woodward report it as found in the 

 beds at Swalecliffe, a mile west of Heme Bay, in East Kent; and in the 

 same deposits at Ilford and Uphall, in South Essex. 



In France it is known from beds of similar age in the Somme Valley. 



HoLOCENE. — In West Kent, the same authors chronicle its occurrence at 

 Maidstone, in a disused chalk-pit, near Otford railway station, and in a 

 deposit on face of chalk escarpment, at Exedown, near Wrotham. In 

 Surrey, at the Horse-shoe deposit, Colley pit, Reigate, the internal granules 

 were very abundant between the 2-feet and 3-feet levels. In Essex, they 

 have been found in the alluvium at Walthamstow. In Berkshire, in the 

 Keimet Valley deposits at Newbury ; and in Oxfordshire at Westbury and 

 Clifton-Hampdeu, near Oxford. 



Parasites and Enemies. — In addition to the numerous enemies of 

 the moUusca generally, Avion ater is internally infested by three different 

 species of Leptodera, a genus of Nematoid worms. Leptodera appendicu- 

 lata, a species remarkable for the possession of a pair of caudal fringes, 

 inhabits the foot of this species while in the larval state, becoming sexual 

 in the decomposing body of the snail at its death. Another species is 

 found in the intestinal canal, and the third species in the salivary glands. 



Fig. 203. — .^n Entozoic Parasite from Arion ater var. rufa X 50 (afier Vah den Broeck). 



Professor Owen records that the larva of a Twiiia is found encysted in 

 the pulmonary sac, which is believed to attain its full sexual maturity only 

 when occupying the intestinal canal of some warm-blooded animal. 



M. Van den Broeck records the abundance of a species of Bntozoon 

 in the intestinal canal of the var. rufa, but which was first detected within 

 the egg of Limax arbm-um. 



