SCIENCE-GOSSIP. 



323 



concerned, but he finds that the red form of Arion 

 atcr is refused by birds in captivity, and hence may- 

 be sematic ( : ). The same authority attributes a 

 _ .„ ....... ._ : .'.:rec: p--y ? L'Ki;ii:.U value (in relation 



to external heat and cold) to the colours in, e.g., 

 and Limax maximus, but the evidence 

 adduced to show this seems insufficient. Scharff 

 says that he has found a claret-coloured variety 

 of Arion attr only in pine-woods where it is very 

 harmonious. Limax marginatum [arborum) looks like 

 a bit of bark on the trunks on which it usually 

 sits. Alitalia tarinata imarginata) assimilates to 

 the ground on which it lives. Arion intermedium 

 (minimus) is like a little fungus just coming out 

 of the ground. " The dark-grey lichens," on 

 which it lives, and among which it sits openly 

 during the day, " with the white and yellow fructi- 

 fication, conceal Geomalaeus maculosus perfectly. 

 There is no doubt that we have here a most 

 striking instance of protective colouring," which is 

 enhanced by the fact that this species lives con- 

 spicuously uncovered. L. E. Adams ( s ) attributes 

 seme influence on the colours cf slugs to "protective 

 mimicry." He adduces no instances, however, and 

 it may be that protective resemblance is meant ( ). 

 W. M. Webb ( Iu ) has recently pointed out the 

 resemblance between contracted specimens of 

 ilia seutulum (and sometimes 'I. haliotidea) 

 with half a broken pebble. 



Having reviewed the significance of the colours 

 which normally occur in our land and freshwater 

 mollusca, we may consider the cases of adventitious 

 protection which have been observed. That 

 se\eral shells (Buliminus, Pupa) cover their shells 

 with bits of dirt, and so conceal themselves, is a 

 very old observation ("). It appears to me, how- 

 ever, that it probably only applies in some in- 

 stances. Buliminus olscuius and Pupa seeale (young) 

 are at least as often found clean as muddy, 

 and even when a considerable quantity of dirt 

 is adhering to their shells are really as easy to 

 see as when they are without it. Where Buliminus 



: lives on smoolh-trur.ked trees, such as 

 the beech, however, it is very probably of 

 service {'■') ; but, as a rule, I think it shuns such 

 open situations, and hides away under stones 

 and other debris, where any protective covering 



be of but little use. I have noticed that round 

 the edges of ploughed fields and in other muddy 

 situation* piultiuola I, Hen covered with 



mud, and so rendered more difficult of deti 

 A similar habit has been attributed to Vanna 



... 



ersnl." 

 Jtf!rt>'« B ' 



peilucida ( ls ), and Succinea — especially, perhaps, S. 

 obionga (")• — is often covered with dirt. 



Among the aquatic species adventitious coatings, 

 probably of some protective value, are common ( 15 ). 

 Old specimens of Planorbis, Linmaea, Paludina, etc., 

 are often covered with a thick algoid and confervoid 

 growth. Measured on the dry, empty shell, more 

 than a year after after collection, when a good, 

 deal had probably been removed by accident, I 

 have found that it may amount by weight to 11 

 per cent, of the dry shell in Linmaea stagnalis, 

 and from 52 to iS per cent, in L. petegra, the 

 two first specimens being very ordinary ones. 

 To my own eyes, at any rate, specimens coated 

 with mud are more difficult to see than these, 

 and are often exceedingly hard to distinguish 

 from accidental nodules of mud or pebbles on the 

 bed of the stream or pond. The nature of 

 the coating varies : it may consist of precipitated 

 CaCO s , which also generally coats some ( 1(i ) of 

 the plants ; or, it may be simply ordinary dark 

 mud, which, either from the water getting muddy 

 from the bottom being stirred up, or by a sudden 

 sinking of the level of the water, covers up the 

 shells. In the latter case the shells which are 

 left high and dry, so long as they do not move, 

 are by this means in all probability considerably 

 helped in escaping the notice of rapacious birds 

 and other enemies. Indeed, I have found Pisidinm 

 in this position almost impossible to collect without 

 entering the water, and thus bringing one's eyes 

 quite close to the mud. The notorious Linmaea 

 tntncatula habitually sits on the muddy bank just out 

 of water, and is nearly always protectively covered 

 with mud. By the nature of the case, the colour 

 of the coating varies, and as a rule harmonizes, 

 with the surroundings. Thus, in a ferruginous 

 pond, where the mud is red, the shells have a red 

 covering too, and where CaCO a is precipitated 

 on shells, it is also precipitated on some of the 

 surrounding objects. The colouring of the shell 

 in Planorbis and Linmaea depends very much on its 

 surroundings during growth. The red colour of 

 Planorbis in ferruginous water is not merely super- 

 ficial, the prismatic layer is tinged red too (E, W, 

 v. Bo well), and the varying tint uf Linmaea 

 seems often to depend partly on inclusions during 

 growth ( ,; J. Si, me species of both (Gastropoda and 

 Ivli 1 . ],r,,;,i 1 I ,1, ,u,i, './ /(in 1 mm, I 1 hlmiu) neai I) 



always sit on the muddy floor with a slight covering 



("I W. E. CollitiK".- In " Zoologist " (j), xiv. p |C 



-.1 I:, ii.ni, 1 ., 1 >, nl . |y gi 111 I. ill) 



,,,,,, Bow It., II the two in dl tlm I; rosli Wi nga al 10 



■ ■ 



1 ' 1 . . 1 • . i.,.i. . 1 1 ■ I. (1891), p. 25. 



[inn I spi nil tlvi 1 spai Ii ■. -" ' v, nl., 11 



otdni tbls prui Ipll n ii,' " iui fai 1 



..1 pai 1 oi tin opi " ilium "i 



• , i- How ' oni bologlst, who wroti ti 



1. .. . 1 dlsti 11. by ml Ml . 'i bl 



... 1 1 1 1 ivo ii ribli 1 1 ■ ibi 



Inclusions Id lbs opi n ulum 



