46 



THE ZOOLOGIST. 



close resemblance to the russet-brown beech-leaves which be- 

 strew the ground, and among which it crawls. The second 

 form, which I call the var. petrea (mihi), is of a light " sun- 

 washed" appearance, with the band very indistinctly marked, 

 closely approximating in extreme examples to the var. albida. 

 This form occurs principally on the more open, stony, bush- 

 covered, semi-precipitous slopes of the escarpment, generally at 

 a higher altitude than the preceding, to which, however, it is 

 similar as regards size. This likewise possesses a remarkable 

 resemblance to its environment, looking wonderfully like the 

 pale yellow oolitic stones among which it exists. 



Although some may be inclined to consider both these cases 

 as protective resemblance, pure and simple, and attribute them 

 to the preponderating influence of the organic environment, I 

 have been compelled to modify the views which I formerly held 

 in this respect in connection with the Lepidoptera (as published 

 in the 'Entomologist' and elsewhere), and have since arrived at 

 the conclusion, from more mature deliberation and practical in- 

 vestigation in the Himalayas and other mountain ranges in 

 Europe and Asia, that the physical environment is a factor of at 

 least equal importance in deciding the morphological characters 

 of animals, though not so potent possibly, except perhaps in- 

 directly, in fixing their geographical and vertical distribution, 

 and this principally in an equatorial or downward direction. I 

 therefore do not consider the two cases described in connection 

 with this king of the Cotteswold Mollusca to be examples of pro- 

 tective resemblance at all, though they superficially possess the 

 appearance of such, but to be due either directly or indirectly to 

 the preponderating influence of the physical environment. In 

 support of this contention concerning the species under con- 

 sideration, I may state that I do not know of any mammal, 

 bird, reptile, or batrachian which preys upon these snails. 

 Thrushes, which are so notoriously fond of Helix nemoralis and 

 H. hortensis, find H. pomatia too large a pill. As far as my 

 somewhat circumscribed experience is concerned, the larva? of 

 certain dipterous flies, and possibly those of some Coleoptera 

 also, are the greatest enemies of the Mollusca, more especially 

 during the adolescent stage and hybernating stage (the diaphragm 

 being pierced with impunity) ; so that protective resemblance to 



