MEANS OF DISPERSAL. 4/ 



such transportal as probable/ and Canon Tristram, 

 in the winter of 1856-7, it is interesting to find, had the 

 good fortune to discover the eggs of some mollusc — 

 probably Siiccinea — attached by their glutinous coating 

 to one of the feet of a passing mallard shot by him in 

 the Sahara, a hundred miles from water ; ^ thus, he 

 remarks, such a bird " might easily carry a Succinea or 

 Physa from Europe to the lakes of Central Africa." 

 It ought to be remem.bered, however, that eggs of some 

 kinds, thus exposed to the atmosphere until dry, would 

 become very firmly attached and so remain even when 

 again moistened,^ so that they would not be easily dis- 

 lodged in a new locality ; but, as many birds probably 

 travel during gales at the rate of thirty-five miles an hour 

 or much faster,^ eggs might certainly be carried before 

 drying to considerable distances, and then when again 

 dipped in water would soon become detached. Many 

 kinds attach their eggs to aquatic plants, fragments of 

 which, we shall see, are likely to be carried by birds. 

 Something may possibly have been done by insects, for 

 Mr. Standen informs me that he once saw, in the 

 HoUinwood canal, an egg-capsule of the river-limpet 

 {Ancylus fluviatilis) attached to one of the wing-cases of 

 an Acilius, a strong flying water-beetle. Some eggs, it 



1 " Island Life," 1880, p. 76 ; ed. 2, p. 79 ; R. Tate, " Land and 

 Fresh-water Mollusks,'' 1866, p. 188 ; H. H. Godwin-Austen 

 " Field," Ixvi. (1885), 499. 



2 See "Zoologist," (3), i. (1877), 260—1. 



3 This happened, at least, to eggs of Lirnncea aiiricularia^ which 

 I exposed on a tin tray and on fragments of water- weeds. 



* "Origin," p. 326. 



