VARIATION AND LOCALITY 133 



the United States northward to the limit of trees— a slightly 

 diversified region of at least ten times the area of California— has 

 only one"! But when one comes to ask how the various forms 

 are adaptational, and how the influences of environment have 

 led to their production, only conjectures of a preliminary and 

 tentative character could be expected in reply. Desert forms 

 are no doubt pallid as in so many instances, and forest forms are 

 more fully coloured, and we may readily enough accept such facts 

 as indications of a connection between bodily features and the 

 conditions of life, but further than that no one can go; so that 

 when we find size, length of ears or of tail, the number of dorsal 

 stripes, the pattern of the colours, not to speak of differences in 

 the pigments themselves, all exhibiting large modifications, we 

 cannot refer these peculiarities to the causation of environmental 

 difference, save as a simple expression of faith. I incline far 

 more to agree with Gulick who, after years of study of the local 

 variations of the Achatinellidae, came to the conclusion that it 

 was useless to expect that such local differentiation can be 

 referred to adaptation in any sense. 17 Even the most convinced 

 Selectionist must hesitate before such facts as those related by 

 A. G. Mayer regarding the distribution of Partula otaheitana, one 

 of these Achatinellidae. The island of Tahiti has been scored 

 by erosion so that a series of separated valleys radiate to the coast. 

 From four successive valleys Mayer collected the species, and 

 found that in the first (Tipaerui) valley all the shells were 

 dextral (115, containing 73 young) ; in the second valley 

 (Fautaua) 54 per cent, of adults and 55.5 per cent, of the young 

 contained were sinistral; in the third valley (Hamuta) 69 per 

 cent, of adults and 73 per cent, of young contained in them were 

 sinistral; and lastly, in the fourth valley (Pirae) all the shells 

 (131, containing 62 young) were sinistral. 18 In connection 

 with these observations I may mention the fact that in a certain 

 pond in the North of England 19 the sinistral form of Limnaca 



17 J. T. Gulick, Evolution, Racial and Habitudinal, Carnegie Institution, Pub- 

 lication No. 25, 1905. 



18 A. G. Mayer, Mem. Mus. Comp. Anat. Harvard, Vol. XXVI, 1902, p. 117. 

 From the tables given I cannot ascertain the actual numbers from the two inter- 

 mediate valleys, but they were considerable. 



19 To which I was very kindly guided by Mr. C. T. Trechmann. 



