TRANSPLANTATION OF UNIVALVES. 87 



was mentioned by Darwin (on Lyell's authority) in the 

 " Origin of Species " in 1859 ; ' in 1876, Mr. E. Duprey 

 stated that he had more than once seen young speci- 

 mens of A. fluviatilis adhering to another common 

 water-beetle, Acilius sulcatus^ and I hear that Mr. 

 Hardy once found a specimen of Dytiscus marginalis 

 with three shells of^. lacustris adhering to the wing- 

 cases^ one on the left and two on the right side. 

 Carried by these insects " from pond to pond," as Lyell 

 and several authors have surmised, the creatures could 

 be quickly distributed, of course, over a large tract of 

 country. That they are occasionally thus carried 

 seems conclusively proved by an observation made by 

 Mr, Standen, who was fortunate enough to detect a 

 shell oi A. fluviatilis upon one of the wing-cases of a 

 Dytiscus caught on the wing after dusk on the evening 



' See "Origin," 1859, pp. 385-6; ed. vi., p. 345 ; I have not 

 been able to ascertain by whom this beetle was taken, and the only 

 mention of the occurrence by Lyell himself, as far as I am aware, 

 is contained in a letter, dated in 1 861, to his nephew, then a boy of 

 ten, who had been finding specimens oi A.fiuviatilis : — " Natural- 

 ists used to wonder how this Ancylus got spread over the country 

 in separated lakes and streams, till someone found a young 

 Ancylus adhering to the elytra of one of those large boat-beetles, 

 Dytiscus marginalis^ which you will see in the collection at Drum- 

 kilbo, and which fly about at night from pond to pond, and may 

 sometimes carry the Ancylus with them, if, like the Patella which 

 you saw high and dry on the rocks here, he can manage to do 

 without water for an hour or two, as most probably he can." 

 " Life, Letters, and Journals of Sir C. Lyell," ii- (1881), 347. 



2 E. Duprey, " Ann. and Mag. Nat. Hist.," (4), xviii. (1876), 344 ; 

 and see also Rimmer's " Land and Fresh-water Shells," (i88o), 

 p. 70. 



