Feb. 27, 1890] 



NATURE 



93 



ovo 



concentric laminae of bone. Thus it is certain that the per- 

 manunity of the bone-corpuscle is very inconsiderable indeed. 

 It may be difficult to define it exactly, but a general consideration 

 of the rapid changes in the shafts of young bones leads me to 

 think it probably much less than a year. 



There is thus a very surprising contrast between the undivided 

 p»ersistence or permanunity of a bone-corpuscle and that of a 

 dentine-corpuscle, which is in various respects so similar to it. 

 While there are numerous instances of very short-lived c >rpuscles 

 in the bodv, I am not aware that until now proof has been 

 offered of the persistence of any living tissue-elements throughout 

 the life of the oi^anism. John Cleland. 



Some Notes on Dr. A. R. Wallace's " Darwinism." 



I HAVE just read this most interesting work, " Darwinism " — 

 seeming to me the clearest and most useful account of the 

 Darwinian theory of evolution ever yet published — and while 

 reading it I have made note of a few matters which I may, 

 perhaps, be allowed t > touch on here. 



On p. 43 are quoted the numbers of varieties of the two snails, 

 HeUx nemoralis and H. hortcnsis, enumerated by a French 

 author — no doubt Moquin-Tandon. These numbers, however, 

 fall far below those actually known at the present day. These 

 snails vary in many ways, but taking variations of handing alone, 

 I know of 252 varieties of H. nemoralis, and 128 of H. hortensis. 



To further illustrate the extreme variability of the MoIIusca, 

 take the varieties of land and freshwater Mollu'^ca found in the 

 British Islands. Of the 88 species of land shells we have 465 

 named varieties, and of the 46 species of British freshwater 

 shells are 251 varieties. So that, excluding probable synonymy, 

 we have about 5 named varieties in Britain to every species of 

 inland mollusc. 



In the same way, the numbers of Rosa and Rubus quoted on 

 p. 77 are below the mark. Of Rosa canina, 33 varieties are 

 known in the British Islands, while the British Rubi number 6^ 

 supposed species. 



A tjood example of a species "occupying vacant places in 

 nature " (p. 1 10), is afforded by the little mollusc Ccecilianella 

 acicula, which is simply organized, and lives in great numbers 

 \xnAe<^^TOVinA {vide NaCttralist, 1885, p. 321). 



The true cause (as it seems to me) of the variability of fresh- 

 water species seems hardly indicated on p. no. All freshwater 

 productions, except those inhabiting large river basins (as the 

 Mississippi), present these peculiarities — they are exceedin^^ly 

 variable and plastic, so that we get few but polymorphic species. 

 Now, for the successful spread of freshwater organisms, it is 

 necessary that they should he. plastic, to adapt themselves to the 

 new environment of every pond or river, and the varieties thus 

 required must not become fixed species, because it is their very 

 changeability under new environment that makes them successful 

 in the struggle for existence and increase. Freshwater forms 

 migrate more than is commonly supposed, and the contents of 

 any pond or river are ever varying. Hence the necessities I 

 have indicated. These points are exceptionally clear in the 

 case of the Unionidce of Europe and North America (see 

 Science Gossip, 1888, pp. 182-184). 



Colorado presents an exception to the rule (p. 112), that two 

 species of Aquilegia are rarely found in the same area. In 

 Colorado we \\z.\& five columbines, viz. A. formosa, A. chrys- 

 antha, A. brevistyla, A. ccerulea, and A. canadensis. But A. 

 Cicrulea is the only one that can be called abundant. 



On p. 139, it is stated that specific characters are essentially 

 symmetrical. Yet the ocelli and spots on the butterflies of the 

 families SatyridcE and LycanidcB surely afford specific characters, 

 and they are frequently asymmetrical (see Entomologist, 1889, 

 p. 6). 



On p. 151, we are told that in Ireland hardly one of the land 

 molluscs has undergone the slightest change. This is not quite 

 true, as the following forms seem to be peculiar to Ireland : 

 Arion aler van fasciata, Geomilacus maculosus vars. allmani, 

 verkruzeni, and andrewsi, Limax arborum var. maculata, L. 

 arborum var. decipiens, Succinea vitrea var. aurea, and S. 

 Pfeifferi var. rtifescens. But these peculiar forms are not more 

 numerous (but less so) than would be found in almost any 

 continental area of equal size. 



The theory (p. 206) that a recent change of food-plant has 

 to do with ihe presence of green and brown varieties of the 

 larva of Macroglossa stellatarum seems hardly tenable, as so 

 many larvae of different species and genera vary in the same 

 manner. 



I have thought (Ent. Mo. Mag., 1889, p. 382) that asym- 

 metrical variation in insects occurred most often on the left side. 

 On p. 217 it appears that the same thing occurs in some Verte- 

 brata. 



On p. 230 the idea of environment directly influencing the 

 prevalent colours of organisms is put aside as improbable. Yet 

 it has seemed that moisture was the cause of a certain phase 

 of melanism, especially among Lepidoptera. Evidence bearing 

 on this point has been given during the last few years in the 

 Entomologist. 



The land shells on the small islands off the coast of Kerry, 

 Ireland, are pale in colour, as I have recorded in Proc. South 

 London Entom. and N.H. Soc. for 1887, pp. 97-98. 



The point on p. 233, about the conspicuous colours of the 

 Aculeate Hymenoptera, seems open to question. In temperate 

 regions, at least, the Aculiuta are mostly of very dull colours — 

 as the Andrenida, many of the Apidcc, and hosts of others. Even 

 the brilliant green Agapostem-jn flies among bright green foliage 

 and yellow flowers, and is not very conspicuous when alive 

 in its native haunts. On the other hand, the non aculeate 

 ChrysididcE and Chalcidida are often exceedingly brilliant in 

 colouring. 



It seems quite doubtful whether the abundance and wide 

 distribution of Danais archippus (p. 238) is due to immunity 

 from parasites, &c., while its migratory habits are a quite sufficient 

 explanation of the facts. Besides, it has at least one parasite — 

 the Pteromalus archif^pi. 



The "progressive change of colour" (p. 298) is well illustrated 

 by the change from yellow to scarlet exhibited by so many 

 groups of species. Scarlet species nearly always occasionally 

 revert to yellow, and there are generally yellow species in the 

 same genus. For details see Proc. South Lond. Ent. and N. H. 

 Soc. for 1887. 



Yellow flowers (see p. 316) seem the most attractive to insects 

 in Colorado, and Mr. F. W. Anderson tells me that the same 

 is the case in Montana. From reasons given in Canadian 

 Entomologist, 1888, p. 176, I am of the opinion that insects 

 cannot distinguish red from yellow. 



It has seemed to me (see p. 359) that the agency of wind in 

 distributing insects is greatly exaggerated, 1 believe whirl- 

 winds may be most important as distributing agents, but ordin- 

 ary gales less so. Many species of insects migrate, but usually 

 during calms. Also (p. 310) the opinion that insects are often 

 carried to the summits of mountains by winds seems to me 

 without sufficient support. Many species of insects live only 

 or habitually at high altitudes, and their presence there is no 

 proof that they were carried there by winds, especially when 

 they are specifically distinct fnm the species of lower regions. 

 Plusia ganuna, on the summit of Mont Blanc, is not very re- 

 markable, as the moth is a great wanderer, and quite capable of 

 finding its own way to high altitudes. Finally, I believe winds very 

 rarely blow tip mountain slopes. I have lived some time at the base 

 of the great Sangre de Cristo Range in Colorado, and although 

 violent winds blow doivn very frequently, I have never obsei-ved 

 an upzvard wind, and residents whom I have questioned are 

 unanimous in saying that they have never known a strong wind 

 blow up the mountains. And the way the trees are bent and 

 twisted at timber-line (11,500 feet), often with only branches on 

 the side towards the valley, well indicates the direction of the 

 winds. 



I think, perhaps, the scarcity of Monocotyledons in the Rocky 

 Mountains (p. 4or) as compared with northern regions, is more 

 apparent than real — the difference indicated in the books being 

 due to the fact that the western grasses are not so well known as 

 the eastern ones. Ferns are rarer on continents than on islands, 

 and the dryness of the Rocky Mountain region is unfavourable 

 to them. 



A giod instance of the effect of environment (see p. 419) 

 recently came under my notice. The polymorphic snail Helix 

 nemoralis was introduced from Europe into Lexington, Vir- 

 ginia, a few years ago. Under the new conditions it varied 

 more than I have ever known it to do elsewhere, and up to the 

 present date I25^varieties have been discovered there. Of these, 

 no less thxu^-^ are netv, and unknown in Europe, the native 

 country of the species! The variation is in the direction of 

 divi-ion of the batids. An incomplete list of these varieties is 

 given in Nautilus, 1889, pp. 73-77. 



It seems doub' ful (see p. 433) how far prickles are a protection 

 from snails and slugs. I found prickles in the stomach of Par- 

 macella (a slug), as recorded in Journal of Conchology, 1886, 

 pp. 26-27. 



