198 



SCIENCE-GOSSIP. 



omata of this species, and comes to the conclusion 

 that it is sematic to sheep. He supports this 

 theory with the following very remarkable facts. 

 In five sheep pastures on the south coast the 

 omata were 46 per cent, of the whole number of 

 caperata ; while in four pastures in which sheep 

 never fed, but which were otherwise apparently 

 similar in character, the omata only amounted to 

 5 per cent. Again, in two areas of the same size 

 (seven square yards) on the Isle-of-Wight downs, all 

 the caperata were collected. In the one in which 

 sheep fed the omata were 61 per cent., while 

 in the other, from which sheep were absent, 

 they only amounted to 22 per cent, of the 

 total number. This is very strong evidence that 

 -the omata form is only extensively developed, at 

 any rate, in the kind of localities examined ( J ), in 

 such places as are habitually frequented by sheep. 

 The natural inference is that the colouring is 

 sematic, and by its means the snails avoid being 

 eaten by the sheep. It is only natural, though it 

 may be wrong, to suppose that sheep would prefer 

 not to eat snails if they could help it, though in 

 some localities they throng the herbage so thickly 

 that it must be a matter of considerable difficulty 

 to get the grass without the snails. It is an old 

 idea that Dartmoor mutton owes its delicate 

 flavour to this strange diet of Xerophila caperata, 

 X. virgata, etc. ( 2 ). It is very possible that the bold 

 markings of X. virgata do a similar service to this 

 very conspicuous species ; though as forms with 

 other markings than bands are comparatively 

 rare, the proposition does not admit of the same 

 demonstration as has been given in the case of 

 X. caperata. 



I suspect, too, that these black or brown and 

 white banded species may be generally cryptically 

 coloured. It is my experience, at any rate, and 

 that of one or two others of whom I know, 

 (especially with A', ericetorum ; X. virgata is easier 

 to- see) that however well the collector knows the 

 shape, size and colour of the species he is looking 

 for, or however plentiful they may be, till he 

 catches sight of one, the ground looks quite fruit- 

 less. When one is seen, one finds out how 

 numerous they really are. This is an example 

 which shows how cautious we must be in saying 

 that any coloration is, or is not, cryptic. It is 

 said that the zebra, with its bright colours and 

 vivid, striped contrast, is very hard to see in the 

 dusk, apart from any question of striped surround- 

 ings. So it would never be imagined, from looking 

 at the two things apart, that the black and white 

 of Xerophila would harmonise in the slightest 

 with the greens and browns of the surface on 



0) In Herefordshire, on road banks and in quarries, the 

 omata form comes to about 3*5 per cent., that is, less than 

 Jidva. 



{-) Borlase (1758), quoted by J . G. Jeffreys, B. C, i., p. 212. 

 J. E. Harting, "Rambles in Search of Shells," pp. 75-76. 



which it lives. All the same, there are reasons 

 for thinking that practically there is a concealing 

 resemblance between these shells and their sur- 

 roundings. There is also another caution to be 

 borne in mind : although they may not be obvious to 

 us, they maybe plain enough to birds. Conversely, 

 a shell which we find no difficulty in seeing may be 

 cryptically coloured with regard to the vision of its 

 natural enemies — birds f 1 ), voles, etc. 



OUR BOTANICAL COMPETITION. 



\\TE cannot pretend to disguise our disappoint- 

 ment at the result of our offer of prizes 

 for a botanical competition, aided by photography. 

 The number of competitors who have sent in 

 examples of their work are far below the limit of 

 ten as set forth in our rules on page 46 in this 

 volume. 



One cause of the small number of competitors 

 was, doubtless, the lateness of the season when 

 the offer was made. Still, those examples we 

 have received are so interesting and have evidently 

 caused such pleasure to the students in botany 

 who have prepared them, that we feel we were 

 right in making the offer. One competitor 

 expresses his "real pleasure and interest in the 

 work, first in seeking out the plants for subjects, 

 then in preparing the pictures, and lastly, in 

 the preservation of the plants for identification." 

 This gentleman's work is so good we sincerely 

 regret the insufficient number of competitors 

 makes it impossible to give the prizes. 



We, however, shall have pleasure in sending to 

 Mr. W. P. Winter, The Science School, Chelten- 

 ham, a consolation prize, his work having been 

 the best. The plants selected by Mr. Winter are 

 more local than rare. His conception, however, 

 of the requirements under the competition is so 

 clear, that we feel we should not let his work be 

 wasted through no fault of his own. Mr. Winter's 

 plants are the deadly night-shade (Atropabelladonna), 

 mountain cranesbill (Geranium pyrmaicum), and 

 snakeweed (Polygonium bistorta). 



Although we have failed this season in drawing 

 ten competitors, the result is so satisfactory we 

 shall next year offer a similar competition with 

 like prizes. — Ed. S.-G. 



Armature of Helicoid Landshells. — Mr. 

 Gude's instalment of this series of articles upon 

 the armature of landshells unavoidably stands over 

 until next month. 



( x ) Is it quite certain that birds do eat Xerophila freely, 

 and that the colours are not sematic? I have never noticed 

 any shell unequivocally broken by birds, but my opportunities 

 for watching the genus have not been very large. J. G. 

 Jeffreys (Trans. Linn. Soc, xvi. (1833), p. 334) has observed 

 that X, pisana are largely destroyed by birds at Tenby ; and 

 .Y. caperata has been taken alive in a wood-pieeon's crop. — 

 H. W. Kew, " Dispersal of Shells " (1893), p. 161. 



