SCIENCE-GOSSIP. 



197 



exactly calculated to produce them, so we find the 

 same species on our English commons offering the 

 same modifications, but in a less degree when 

 compared with the ordinary run of dark- and damp- 

 loving species. That the disadvantages of tempera- 

 ture under which species from arid situations 

 labour are fully compensated, is shown also by the 

 extraordinary abundance in which Helix lactea, H. 

 descrtorum, as well as Xerophiia in England, occur 

 in such situations ( 1 ). Strobel has shown that 

 exposure to dryness and warmth induces leucoch- 

 roism in X. virgata (-). 



The thick shell also serves the same end by 

 hindering evaporation 1 ; ). The increase in thick- 

 ness, as pointed out above, is really not very great. 

 It is possible that the question of opacity is of 

 importance. All, except in a small degree Xerophiia 

 urn and Frutickola carthusiana ( 4 ), are practi- 

 cally opaque : but there is no necessary dependence 

 of adiathermacy or opacity, and there seems to be 

 no data on which to come to a conclusion on this 

 point. 



It is an old observation of Bouchard-Chantereaux 

 that Xerophiia virgata never hibernates, and the 

 statement has been repeated on his authority in 

 several places (»). There are some grounds for 

 supposing that this is not strictly so as applied to 

 the whole group. For instance, J. W. Horsley (°) 

 has recently recorded Tachea hortensis well out and 

 active in April, while Xerophiia virgata and caperata 

 were still hibernating. I have myself noticed 

 during last winter (1896-7), which was a very mild 

 one. that a colony of X. trieetorum were hibernating 

 in comparatively warm weather, They were first 

 observed (near Kenchester, Herefordshire) on 

 October 9th, 1S96 : but no live specimens could be 

 found on November 9th, nor again in December. 

 It is possible that this phenomenon was due to the 

 fact that they occurred on an ordinary hedge-bank, 

 and the ground-colour of the shells, which were 

 very thin, was certainly not white ( T ). On the 

 other hand, I have seen A', caperata crawling about 

 on moss when snow lay quite thick on the ground. 



1 \ " Fundamenta." pp. 31 ft. L. E. 



caperata on the desert at Bagdad 



'ill>. I.. B. Poulton, 



; 



'Oi). P- 93- 



- .-' titicola 

 ■ i " more lolld " and it 

 "dry • ■• '"eys. U. C. I., p. 199), an obser- 



vation wUk 



eeially In somr localities. It Is frequently quite 



'. . I., p. 212. 



sua' statement. Journ. ol 



''lack, or to thick, at 

 Its* 01'.' 



rsttrtl .- fhtta will stand 



. Il 



F. V. Theobald (') confirms the statement that 

 A*, virgata does not hibernate ; and Mr. E. W. W. 

 Bowell tells me that near Sissinghurst, Kent, he 

 finds that though A', virgata "is to be found in the 

 depth of winter, it disappears in March and April." 

 There thus seems some grounds for supposing that 

 these snails can withstand, with comfort, a con- 

 siderable degree of cold. 



Albinism, which is a more frequent mode of 

 variation in these six species than melanism, is an 

 accentuation of their normal tendency, and only 

 further adapts them to their manner of life by the 

 methods indicated. 



Regarding the form with a white ground-colour 

 with a few definite dark-brown or black bands as 

 the typical one (-) in this group, we find that it is 

 an uncommon one in X. caperata. This species 

 very frequently, normally in fact, has the band 

 above the periphery (i.e. the most conspicuous 

 one) broken up into spots ; and while this mottled 

 form often has a white ground-colour, it is very 

 frequently a rather dirty, dingy yellow, in which 

 case also the markings may be dull and ill-marked 

 or even absent. This form occurs in places 

 other than those in which Xerophiia is normally 

 found. It occurs on hedge-banks and in fields 

 where the herbage is long and coarse, and is 

 by no means confined to situations which have 

 a mere skin of vegetation. Hence it is not so 

 much exposed to heat and, in a less degree, 

 to cold as the others. So far from suffering 

 any great hurt in this direction from its loss of 

 albinism( i; ). it seems to derive an immediate gain. 

 This is the only case I have personally come across 

 where cryptic coloration, real or supposed, has 

 deceived me. I have repeatedly, in localities where 

 this dull, dirty-yellowish, more or less monochro- 

 matic form occurs, mistaken for shells the withered 

 heads of flowers, e.g., Ccntaurea nigra, broken ends 

 of bits of stick, and other objects of a similar 

 appearance. The mottled form, with a bright white 

 ground-colour, affects open situations on bare banks, 

 and especially, as far as my own experience 

 goes, quarries, where it is a conspicuous object. 

 Especially is this so where it occurs in myriads 

 on some dry gravelly place with scarcely a single 

 blade of grass. The number of dead specimens 

 occurring in these situations is remarkable. 



S. S. Pearce (') has carefully studied the form 



/ .ologlst " (3), xix., p. 207 (1895). 



C)S. ' Pi tea Mourn, of Concb., vl., pp, tsvnj) considers 



that all forms of Aerof hita 1 uperata arc derived from a uni- 



bell -""1 tbal the ornata form arises from a 



mottli 'i marking 1. ( . Ashford [ibid. 11., pp , i, 



iht 1 band, ii"i'i tEai tin- band .<i bi perlpberj Ii 



•pllttlng scrot 1 Into I" sd 1 and <ii isppi at Ins 1 . " 1 be discon- 

 tinuity >A tic; bands mi caperata appears* '" be largely due to 



Ol Ibl hell." — I'.. VV. W. BOWI 11 



i'i Which may bo Increased by a superficial ooatlng ol 

 dirt. 



I'I JO'.' 



» I 



