122 THE DISPERSAL OF SHELLS. 



island may not be a very rare event. It cannot be 

 supposed for a moment, however, that they will often be 

 landed in spots suitable for the establishment of new 

 colonies, for drift-timber, etc., is only likely to be thrown 

 well out of the reach of high tides by violent storms. 

 Even when this happens it is quite likely that an immi- 

 grant would be picked up at once by some hungry bird, 

 or it might find the soil, the climate, or the food-stuffs 

 altogether unsuitable, and even if it survived and bred 

 for a time, it might be unable ultimately to com- 

 pete with the molluscs already inhabiting the spot, 

 or to withstand the attacks of new enemies surrounding 

 it. Even under the most favourable conditions a few 

 imported individuals would very likely lose sight of 

 each other, and die, consequently, without leaving off- 

 spring ; and this fate would surely happen to solitary 

 specimens, unless they chanced to contain fertile 

 ova. Occasionally, however, in the course of ages, 

 colonies have almost certainly been thus established, 

 perhaps by solitary individuals. The facts above 

 referred to concerning the production of fertile eggs by 

 snails which had long remained dormant are of interest 

 in this connection ; one can well imagine, for instance, 

 that the thirty " points " with which the solitary Helix 

 observed by Mr. Gaskoin became surrounded might 

 have founded a colony at some distant plac^, even if the 

 accidents leading to the transportal of the parent had 

 obliged it to remain without food, in a torpid state, for 

 a long period, provided of course that the offspring of 

 the same parent can multiply inter se. It will be 



