MEANS OF DISPERSAL. 1 5/ 



Sir C. Lyell, remarking on the wide range of 

 Succinea putris, a land-shell which inhabits moist places 

 on the borders of pools and streams^ suggested that 

 water-fowl might have distributed its ova entangled 

 among their feathers/ and it seems quite likely that ova 

 of certain terrestrial kinds may be occasionally thus 

 carried, either in the feathers or on the feet of birds ; 

 indeed, we have a near approach to proof of such 

 transportal, the Rev. Canon Tristram, as we have seen, 

 having once found ova, believed to be those of a Succinea, 

 upon one of the feet of a mallard shot by him, on the 

 wing, in the desert of Sahara.^ It is doubtful, however, 

 whether Succinecu, from the nature of the localities they 

 often or usually inhabit, ought not, for the present pur- 

 pose, to be classed with fresh-water, rather than with 

 land-shells. Mr. Darwin suggested that the just- 

 hatched young, possibly, might sometimes crawl upon 

 the feet of ground-roosting birds, " and thus get trans- 

 ported ; " ^ and it certainly seems in the highest degree 

 probable that such is the case, but, as far as I know, 

 no observations in support of such a supposition have 

 yet been made. In one of his letters to Wallace, 

 Darwin mentions having been interrupted when begin- 

 ning to experiment on the point.^ As was mentioned 

 in chapter ii., small quantities of earth are occasionally 



1 " Principles," ii. p. 377- 



2 H. B. Tristram, " Zoologist," (3), i. (1877), pp. 260-1. 



3 "Origin," p. 353 ; and see " Geographical Distribution," i. pp. 

 31-2. 



^ " Life and Letters," iii. (1888), p. 231. 



