OF LIFE IN GENERAL. 315 



Rhine, and at Bonn and in the still lower reaches the 

 red of the snail deepens to a chocolate brown. Cock- 

 erell* also has noticed how sensitive is this species of 

 snail to a changed environment. Thus it was intro- 

 duced from Europe into Lexington, Virginia, a few 

 years ago, and has since then varied extraordinarily. 

 Already, in 1890, 125 varieties had been discovered in 

 this locality. Of these no less than 67 were new, and 

 unknown in Europe. The variations noticed by Gu- 

 lick t in the land snails of the Sandwich Islands may 

 also be due partly to the effects of environment. In a 

 small forest region about forty miles by six miles in 

 area, in the Island of Oahu, Gulick found about 175 

 different species, represented by 700 or 800 varieties. 

 Successive valleys often showed allied species belong- 

 ing to the same genus, and Gulick noticed that in every 

 case, " the valleys that are nearest to each other fur- 

 nish the most nearly allied forms; and a full set of the 

 varieties of each species presents a minute gradation of 

 forms between the more divergent types found in the 

 more widely separated localities." Only a very few of 

 the species ranged over the whole Island, most of them 

 extending over only five or six miles, and a few over 

 only one or two square miles. These variations did not 

 appear to be due to the action of the environment, as 

 the food, climate, and enemies in the different valleys 

 seemed to be the same. Also the snails on the rainy 

 side of the mountains did not differ any more from 

 those on the dry side than they did from those inhabit- 

 ing a neighbouring wet valley an equal distance away. 



* Nature, vol. li. p. 393. 



f Journ. Linn. Soc. (Zool)., vol. xi. p. 496. 



