122 



HARDWICKE'S SCIENCE-GOSSIP. 



noun as " conditions " is not good English, and that 

 the phrase as it stands means nothing. Mr. Williams 

 no doubt intended to convey the principle contained 

 in the following passage from Darwin : — 



"All fresh-water basins taken together make a 

 small area, compared with that of the sea or land. 

 Consequently the competition between fresh-water 

 productions will have been less severe than else- 

 where, new forms will have been then more slowly 

 produced and old forms more slowly exterminated."* 

 (4.) Mr. Fryer's argument that white cannot be an 

 advance in colour, is very good, and there are 

 instances in which colour must have preceded 

 albinism. Mr. Poulton thus speaks of the case of the 

 albino peacock : — 



"The regions in which 'structural' colours 

 usually appear are readily recognisable, the white 

 being of a different quality, the ' eyes ' on the train 

 coming out like a white damask table-cloth. 



' ' Doctor Gadow informs me that the same fact is 

 true of white ducks and drakes, the wing coverts, 

 which are blue in normally pigmented individuals, ex- 

 hibiting a peculiar sheen or gloss differing from the 

 rest of the plumage. Doctor Gadow states that the 

 structural colours are absent because the existence of 

 a pigment beneath is necessary in order to show them 

 off; and he points out that the ancestors of birds 

 with such structural colours cannot well have been 

 white because the effect depends in part upon pig- 

 ment."! 



(5.) There are in the writer's collection specimens 

 of Helix rufescens in which the nucleus is of a darker 

 brown than the rest of the shell. 



Most specimens which he possesses of Helix arbus- 

 torum, H. nemoralis, //. hortcnsis, H. aspcrsa and 

 H. Pomatia have a nucleus agreeing in colour with 

 the " ground-tint " of the shell, thus in yellow, buff 

 or brown examples of Helix nemoralis the apical 

 whorl is correspondingly yellow, buffer brown. 



Specimens of Helix Fisana from Tenby, Jersey, 

 Guernsey and South Portugal have nuclei of a very 

 dark brown colour, approaching black. 



Of Helix virgata, H. ericetorinn, H. caperata and 

 H. acuta the nucleus is brown, corresponding in 

 colour with the bands. "White specimens of H. 

 Pisana, H virgata and H ericetorum are also in the 

 writer's possession which have no bands developed? 

 but which nevertheless, retain the dark brown 

 nucleus. 



(6.) This paragraph depends on No. 4. The case 

 of albino individuals of banded Helices is analogous 

 to that of the white peacock which shows the " eyes " 

 on its train, for in normal specimens of these snails 

 the colours of the bands are accompanied by 

 structural peculiarities in the shell, and in albino 



* "The Origin of Species," by Charles Darwin, F.R.S., 

 6th edition, p. 83. 



t "The Colours of Animals," by E. B. Poulton, F.R.S., 

 note on p. 329. 



forms the areas normally pigmented are marked by 

 transparent zones. Therefore the whiteness is not 

 a primary but a secondary feature. 



(7.) Although Mr. Williams seems to have the 

 best of the argument with regard to the immediate 

 derivation of Cyclostoma elegatis, it must be pointed 

 out that the occurrence of this shell in Pleistocene 

 fresh-water deposits is no argument in favour of his 

 view, for truly, terrestrial forms abound in such 

 deposits,"" that its colours no more support the theory 

 than do those of the Helices. The SuccinecB can 

 hardly be called fresh-water species ! 



(8.) What Mr. Fryer says with regard to the 

 colours of the Hyalinia: and Helices can in eveiy way 

 be endorsed by the present writer, who has given 

 his attention to the subject for some years, and hopes 

 to soon publish his conclusions with the evidence on 

 which they are founded. 



(9.) It is very probable that bands represent 

 coalesced spots, the stripes of mammals in several 

 cases undoubtedly originate in this way, but some of 

 the species which Mr. Williams mentions, such as 

 H. aspersa and H. virgata (other snails. Helix Pisana, 

 H. acuta and H vcrinicidata may be added) which 

 have bandssome times represented by dots,t have only 

 gained this style of marking secondarily, after the 

 bands had already been evolved, for the apparent 

 breaking up of the bands on these shells is due to the 

 presence of striag which really only obscure the band 

 underlying them. The writer has tested this by 

 cutting sections of the shell of Helix aspersa, also by 

 scraping off the prominences from the same species 

 and from H. vermiadata, and has since found that, 

 Mr. Charles Ashford calls attention to this point. J 

 Mr. Ashford is perhaps one of " the few who have 

 published their thoughts on this matter," but whose 

 names are not given by Mr. Williams. 



(10.) On taking into consideration the passage 

 from Darwin quoted in No, 3, Mr. Williams's 

 meaning will become clearer. 



(11.) Mr. Fryer's references go to show that 

 field-naturalists are not all of Mr. Williams's opinion 

 with regard to the enemies of the genus Hyalinia. 

 Paul Fischer, it may be noted, puts this genus with 

 the Limacidse not with the Helicidffi as does Mr. 



Pace. 



The criticisms as yet offered on Mr. Williams's 

 paper have necessarily dealt not so much with his 

 theory as with the facts supposed to support it. That 

 these facts have little or no bearing on the matter, is 

 the conclusion that has been arrived at, and it is not 

 difficult to point out the weakness of the theory 

 itself. The manner in which the shell of the marine 

 ancestors of the land and fresh-water molluscs was 



* " The Pleistocene (Non-Marine) IMoUusca of the London 

 District," by B. B. Woodward, F.G.S., F.R.M.S., &c., 

 " Proc. Geol. Assoc." vol. xi., No. 8 (iSgo). 



+ "Darwinism," by A. R. Wallace, LL.D., F.S.S., p. 289. 



% " The Journal of Conchology," vol. iii., pp. 84-98. 



