140 RANGE OF ^OLOSOMA. [CH. Ill 



emerge from a single cocoon, the lower worms often 

 emerge in great quantities from a single cocoon ; a single 

 cocoon therefore conveyed to a new locality may be the 

 means of founding a perfectly flourishing colony. The 

 little genus <sEolosoma, distinguished by the brilliantly 

 coloured oil globules with which the skin is ornamented, 

 has, so far as regards one species at any rate, the power of 

 temporarily encysting itself 1 , it has thus a double chance 

 of carriage to a distant locality at the hands or rather at 

 the feet of birds. We find that these facts are in 

 accordance with the actual distribution of the animals 

 concerned. Earthworms as a rule are not found in 

 countries unless there is a reasonable probability of their 

 having reached them by their own efforts in traversing 

 the soil, while the aquatic Oligochaeta are often very widely 

 distributed. I have given a few instances of this above. 

 It has been also pointed out that many of the aquatic 

 Oligochseta possess other means of dispersal by birds in 

 addition to the cocoons. The setae are often such as 

 would readily adhere to any rough surface, owing to their 

 hooked and bifid tips and their considerable size in 

 proportion to that of the body. 



Dispersal of land and fresh-water Mollusca. 



This subject has been so recently and fully treated by 

 Mr Kew 2 that it is only necessary to make a few extracts 

 from his book. The extension of their range on the part 



1 Cf. Ann. and Mag. Nat. Hist. Jan. 1892, p. 12. 



2 The Dispersal of Shells. Int. Sci. Series, London, 1893. 



