SCIENCE-GOSSIP. 



343 



COLORATION AND VARIATION OF BRITISH 



EXTRA-MARINE MOLLUSCA. 



By Arthur E. Boycott. 



{Continued from page 325.) 



XT OT much is known as to any variation in the 

 body pigments correlated with variation in 

 shell coloration. Mr. Bowell has, however, made 

 the following very interesting observations : "There 

 are two pretty constant sires of melanin globules 

 in the pigment cells of Tachca : A are about 3 n 

 diameter. B about 05 to o 75 ^. .-I occur only 

 in small numbers, or not at all. in lilacinae, 

 •■{ and light purplish banded fasciatac, 

 B being numerous. Both A and B occur in 

 ordins.: \ but in very dark specimens A 



greatly preponderates in numbers." 



L. E. Adams (') has exhibited an albino of 



us asfasus, with pink eyes(-), with an 



unusually dark shell, from Northampton. This is 



an important specimen, as showing a pigmented 



shell without pigment being apparent in the mantle. 



Limnaca slagmalis produces a pigment which is 

 chiefly found in specimens which are functionally 

 male, and appears to be derived from some part of 

 the sexual apparatus. When hot water is poured 

 over a functionally male adult specimen ('), the 

 fluid is ejected from the genital orifice. It quickly 

 turns from rose colour to light purple on exposure 

 to the air, and finally fades. Traces of it may 

 often be seen on the columellae of specimens in 

 collections. Similar pigments seem to be secreted 

 by PUu :'■■:: : mplanatus, Limnaca palustris, and, in 

 a less degree, by L. f nigra (') ; also, perhaps, by 

 Paludina ami To these are probably due 



the vars. tixcta, Jeff., roseolabia'.a , Jeff., and, in part, 

 (jmelin, of Limnaca falustris. as well as 

 Wolf, of L. stag- 



Tachca korlensis often has a pink, and Ctyptoi 1 

 ■ \. peristome ; and, less frequently, the rib of 

 teveral species, t.g , Fruticicola hisfida, Xerophila copt ■ 

 tinged with pink. This appears to depend 

 very much on the weather l.ast year (i8'/>) such cases 

 appeared commonly in the autumn in Heri 

 shire, after the exceptionally rainless eight months, 

 from January to Aogasl ] G Jeffreys long ago 

 observed that " the beautiful pink gloss observable 



Mr. Adams lia< 

 n in LtmaM maximui, 1 



■ 1 dm 10 



ApUxit 



■ ila |ilnk ih 



nl> l> 





on the mouths of X. pisana and X. virgata is 

 entirely owing to the action of and their exposure 

 to the sun. In the specimens found in more shel- 

 tered situations, the colours and markings are much 

 fainter, and sometimes altogether wanting" ( G ). 

 It is well known that Draparnaud produced a 

 similar result by starvation. It is a matter of 

 common observation that parts of the sexual 

 apparatus, e.g., the dart-sac, are often tinged in 

 Tachca and other snails with a pale pink or purplish 

 pigment ('). 



The inside of Unio pictorum is often tinged with a 

 beautiful pink colour : of 136 specimens from the 

 Hereford Waterworks (1S9G), sixty-one per cent, 

 (excluding very young ones) were pink inside with 

 a bright yellow periostracum, while the remaining 

 thirty-nine per cent, were white inside with a dull, 

 greenish-yellow periostracum. It seems that the 

 difference, which was very striking, is probably 

 physiological, not morphological, and may be 

 sexual. Rogers has attributed a similar pheno- 

 menon in a canal near Manchester to the " refuse 

 at the bottom " of the water ( H ), and the form 

 has been frequently recorded. The nacre in 

 U. tumidus may be similarly tinged, but the pink 

 is not quite the same, and I have more often seen 

 this latter species with white or pale violet-purple 

 nacre than pink. In U. tumidus the pink is stronger 

 in hot seasons, and may be increased by "over- 

 cooking " (E. W. W. Bowell). 



By the kindness of Mr. J. T. Nance, of Halliol 

 College, Oxford, some of the white and pink 

 ' '.pictorum, from Hereford, above referred to, have 

 been analysed, and he is of opinion that the red 

 colour is due to a trace of manganese (■') too small 

 to estimate quantitatively ; at any rate the red shell 

 gave a strong, and the white shell no, manganese 

 reaction. Both shells contained a trace of iron, 

 and it seems fairly certain, judging from its 



rrana. Linn. Soc. xvi. (1H.13), p, 134. 0. F. Miillor 

 (Venn. Hist. II. (1774), p Go, says, "margo roneua." 



over, wai m, di v p ars (auch 1 1 IgG 



in Herefordshire li to produi 1 1 ti ndi ni 1 10 alblnli m on 



. || In, , ■ r./ii r/i mi . c/. " Brltlah Naturalist," 

 ■ 121. 



| 1 ■: mi 0/ . I p 



■ nol erj 1 n In mi llui 1 Q 1 



li. if ach Mn, and Cu Is al tab onl ii"in ilio 



bi Ini i mi mi 1 . ai 1 oppoi 



1 ■ 1 pari In f hi Blood that li '"' 1 '" 



1 Griffith's " Pbyilolojzy ol lnvorti 



1 li I hi bl I ol ' "i italn 



b-Bi ni but Di Ilns i" llillll 11. 



' I 1, ,. ! |,(1 J) p 1 I HI ll" 



,,,. . (and olhei mi ml I In iho animal 



I.Csub I rsdi III ogl( Blologlque (1 I97), 



J . II. 



