226 



SCIENCE-GOSSIP. 



attack, and invariably forced them to retreat. The 

 immature birds repeatedly rose and circled about 

 the loch, keeping entirely clear of the surface, and 

 clanging in flight. 



I passed from the gullery to the road which runs 

 along the north-east side of the loch, and in 

 skirting the water's edge I met with the common 

 sandpiper, and noted a party of tufted ducks and 



a single goldeneye on the water. At the head of 

 the loch, the byroad joins the main road for 

 Stromness, but before returning thither, I visited 

 another water of fair size, Clumly Loch, on 

 which I did not find the bird life to differ 

 much from that noted on the lochs already 

 described. 



(To be continued.) 



COLORATION AND VARIATION OF BRITISH 



EXTRA-MARINE MOLLUSCA. 



By Arthur E. Boycott. 



(Continued from page 198. ) 



"PASSING over Arianta, Cryptomfhalus (? cryptic 

 on or by walls, etc.) and others about which 

 no very striking suggestions have been made, we 

 come to the conspicuous group comprising the two 

 species of Tachea. It is here that bright pigmenta- 

 tion is most developed in British terrestrial species, 

 and there have naturally been many suggestions 

 made to account both for the brightness and variety 

 of the colours. These colours are often, especially 

 in Tachea, ncmoralis, accentuated by the contrast of 

 black bands, which bands play some part in many, 

 if not all, of the theories which have been put 

 forward concerning the group. In certain isolated 

 cases the colours appear to be cryptic. Thus, 

 Mr. A. W. Brown tells me that he has on several 

 occasions noticed a striking resemblance between 

 a red-brown form of Tachea and the dead beech 

 leaves among which it is found. This seems to be 

 the var. fagorum, of Weinland, referred to as an 

 example of cryptic coloration by J. W. Taylor ('). 

 But it can hardly be supposed that the ordinary 

 reds and yellows occurring in the usual situations 

 are cryptic. To us, at any rate, and also apparently 

 to thrushes, blackbirds, etc., they are exceedingly 

 obvious, though my brother tells me that he has 

 often found the dark, five-banded rubella form of 

 T. nemoralis difficult to detect on a roadside bank (-), 

 especially at dusk. The possibility of coloration 

 being nocturnally cryptic must always be borne in 

 mind when considering species which chiefly move 

 during twilight and darkness, just as in considering 

 epigamic colours we must own that our knowledge 

 of colour-vision and aesthetic sense in mollusca 

 (and in birds, etc., for cryptic and sematic colours) 

 is very incomplete. 



It has been ingeniously suggested by W. H. 

 Dall, "that the tendency to striped markings 

 would probably aid in the concealment of the 



(i) Monograph, part ii., p. 94 (1S95). 



( 2 ) I suppose the preference which Tachea shows for road 

 banks overthose in fields is because of the greater abundance 

 of varied and coarser herbage on the former, while the latter 

 are generally very grassy, and, which may also have its eflect, 

 more eaten over by cattle. 



shells among the lights and shadows of the grass 

 and herbage" (•"). John T. Carrington ( 4 ) has 

 advanced what seems to me a capital objection 

 to this theory, viz., that " when the animal is at 

 rest or feeding, with few exceptions, the natural 

 position of the stripes on the shells is across the 

 grass and not in the direction of its growth," 

 though, of course, some of the stripes run much 

 in the same direction, and a practical re-examina- 

 tion has made me less certain than I was that the 

 majority are transverse. F. E. Beddard (•') says 

 the colour is either sematic or epigamic. He 

 very naturally objects to regarding them as 

 epigamic in hermaphrodite, but not, it must be 

 remembered, as a rule, self-fertilizing animals. 

 Indeed, differences in shell-form has been 

 definitely associated with sex only in very few 

 of the species in which the sexes are separate, 

 and Eimer and C. Darwin ( 6 ) are agreed that 

 sexual selection has not modified mollusca. That 

 they are not sematic in character is sufficiently 

 evidenced, I think, by the fact that such quantities 

 are destroyed by birds. Everyone knows the 

 "thrushes' stones" at which the birds immolate 

 their captures, and, though perhaps more abundant, 

 though it may be very likely only more obvious, 

 in winter, they are common enough in summer, 

 which shows that the birds are really fond of this 

 diet, and are not merely driven to it when softer 

 and more succulent food is absent ('). I have, too, 

 noticed very well-fed fowls picking Fruticicoia ru- 

 fescens out of a rockery with evident delight. 



It seems going a long way to suggest that the 



(») J. W. Taylor, " Monograph," p. 95. 



(<) Science-Gossip, N.S., iii. (1896). P- 123. For an 

 illustration see "With Nature and a Camera," K. and C. 

 Kearton(i897), p. 294. 



(5) "Animal Coloration" (1892), p. 56. I should like to 

 say that it was through no fault of mine that Mr. Beddard 

 was misquoted (" cryptic " for " sematic ") in the " Zoologist " 

 (3). xx. (1896), p. 68. 



( 6 ) " Descent" (1S71). 1., P- 326. , 



(") A decrease in the abundance of Tachea and Arianta 

 round Manchester has been partially attributed to the 

 increase of blackbirds and thrushes.—" Conchologist, ' 1. 

 (1891), p. 29. 



