36 



THE BRITISH NATURALIST. 



[Febeuary 



That when once produced, this banding, like other pecularities, tends 

 to become hereditary, is abundantly proved by the numerous examples 

 of this form found in many districts. Had another individual with 

 the same peculiarity been produced in the same neighbourhood and 

 these paired we might have had the var. established in this place. 



Dr. Hauesler has bred the beautiful white V3.nety oi Pupa dolm7n 

 for several years, removing all those which were coloured, so as to 

 breed from white individuals only. A short distance from Tuxford 

 there is a field in which the white var, of H. hispida is abundant, and 

 at one spot the prevailing variety. For several years I have, from 

 time to time, visited this field, and I believe the whites are becoming 

 more common than formerly, their breeding with the common forms 

 has resulted in shells of all shades. I have recently arranged a series 

 from pure white gradually darkening till almost the darkest hues of 

 this species are reached. 



Many varieties are determined during the life of the individual by 

 environment, temperature, the nature and quantity of the food supply, 

 &c. I may mention the forms with reflected lips as well as those 

 decollated forms mentioned last month, the eroded shells frequently 

 found among fresh-water species, thick and thin shelled vars., and the 

 large and minute forms, the latter probably dependent on the 

 abundance or scarcity of food, and also on climatic influences, the latter 

 cause appears to aff'ect individuals in various degrees, just as among 

 ourselves some stand hot summers or severe winters better than others, 

 they are also, when the conditions producing them are permanent^ 

 transmitted to the offspring producing apparently permanent races. 

 As an example I will mention the monster B. decollntiis var. maxima of 

 Algeria, these measure 50 by 20 mm., while the ordinary form in 

 Europe measures only 25 mm., the var. major from the same country 

 measures about 35 mm. M. Ancey informs me that a form somewhat 

 resembling that of Europe occurs sparingly in some districts, and that 

 in the Sahara a small thick shelled form is found, not much decollated, 

 these varieties are never found together. 



As an example of diminution of size I may mention the var. 

 seryatina of Pupa secale from the Pyranees, measuring only 7 mm., the 

 ordinary British examples being 8 to 8.5 mm. in length. Although 

 mountainous districts seem the proper homes for the pigmy vars., a 

 curious instance of the contrary is seen in a list of shells from Formosa 

 published by Mr. Damon, in which he mentions a large form of Helix 

 formoscnsis from the mountains, and a small var. from the valleys of 

 that country. 



As an example of a change of size produced under altered 

 circumstances I relate the following: — In September, 1884, I received 



