June 6, 1878] 



NATURE 



141 



simply natural selection ; but Mr. Wallace regards this 

 view as erroneous, and to him the very frequent supe- 

 riority of the male bird or insect in^brightness of colour, 

 even when the general coloration is the same in both 

 sexes, seems to be due primarily to the greater 

 vigour and activity and the higher vitality of the male- 

 He reminds us that the colours of an animal usually fade 

 during disease or weakness, while robust vigour and 

 health add to their intensity. This intensity is most 

 developed in the male during the breeding season. It is 

 also very general in those cases in which the male is 

 smaller than the female. This greater intensity of 

 coloration in the male would be further developed by 

 the combats of the males for the possession of the 

 females. Increased vigour, acting thus on the epidermal 

 system, would soon produce further distribution of 

 colour, and even new tints and markings. Nay, even the 

 remarkable display by so many male birds of their pecu- 

 liar beauties of colour and plumage may be thus ac- 

 counted for ; for at the pairing season these birds are in 

 a state of the greatest energy. Even unomamental birds, 

 at such a season, flutter and spread out their wings and 

 erect their head-crests or their tail-feathers ; and there 

 would be a progressive development of these ornaments 

 in all dominant races, and if those portions of the 

 plumage which were originally erected under the in- 

 fluence of anger or fear became largely-developed and 

 brightly-coloured, the actual display under the influence 

 of jealousy or sexual excitement would be quite intel- 

 ligible ; the males would soon find what plumes were 

 most effective, and would endeavour to excel their rivals. 

 It will thus be seen that Mr. Wallace's theory of 

 colour might almost be called a molecular one. The 

 causes of colour are due to molecular or chemical changes 

 of certain substances, and on the action on these of light, 

 heat, and moisture. They can be produced or intensified 

 by processes of development, and this as the surface 

 bearing these colours is extended or diminished and as 

 there is a surplus of vital energy ; or they may be, as in 

 plants, acted on by some, as yet, unknown local action 

 dependent on the soil or on vegetation. 



Doubtless this theory will give rise to much contro- 

 versy; and in the course of this, no doubt, many import- 

 ant facts will be elucidated. Thus, Mr. Wallace reminds 

 us that, in the case of those female birds with brighter 

 plumage than the males, the females are larger, more 

 pugnacious, and show more of vital energy. 



One portion of tropical nature Mr. Wallace has over- 

 looked in the volume — that which spreads its brilliant 

 colouring over the white rocks that lie under the sea. 

 Crowds of lovely forms are here ; and they are worthy of 

 a chronicle. E. Perceval Wright 



I 



LETTERS TO THE EDITOR 

 \The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 [The Editor urgently requests correspondents to keep their letters rtf 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearatue even of com- 

 munications containing interesting and novel facts.l 

 Extinct and Recent Irish Mammals 

 Prof, Boyd Dawkins, in his interesting "Preliminary 

 Treatise on the Relation of the Pleistocene Mammals to those 



now living in Europe," just published by the Palaeontographical 

 Society, places the Irish elk {Cervus megaceros) among the pre- 

 historic mammals in consequence of its presence "/« the peat 

 hogs of England, Scotland, and Ireland ; " indeed, in a former 

 monograph on the British Pleistocene Mammals, by Messrs. 

 Dawkins and Sandford, and published by the same Society, it 

 is stated that "the C. megaceros, C. tarandus, C. elaphus, and 

 Bos longifrons, have been found associated in peat in Ireland.^^ 



Now although remains of the red deer and short-horned ox 

 are not unconmion in Irish turbaries, there is not a single 

 authenticated instance of either the Irish elk or reindeer having 

 been discovered in peat. This observation as regards the Irish 

 elk was made by Prof. Owen long since (1846) in the " British 

 Fossil Mammals," and a wide field of observation confirms my 

 impression of its truth as far as Ireland is concerned. More- 

 over, there is no reliable evidence to show that man and the 

 Irish elk, reindeer, mammoth, horse, and bear, were contempora- 

 neous in this island. 



With reference to the smaller Irish mammals referred to in 



j Mr. Dawkins's treatise. On the authority of Wilde and others 



it is stated that both the Martesfoina and M. abietum are natives. 



The former, at best a doubtful British species, has never been 



authenticated in Ireland, but the latter is not uncommon. 



Again, neither the weazel {M. vulgaris) or polecat {^. pa- 

 torius)ha.ve any claims to be included in the Irish fauna. As to 

 Eelis catus there is much doubt, the individuals being in all pro- 

 bability domesticated cats run wild. 



In regard to the rodents given in Mr. Dawkins's list as Irish, 

 neither the Arvicola agrestis nor the Arvicola amphibius have 

 been identified ; but on the other hand, the house mouse (M. 

 musculus), reported absent, is unfortunately too plentiful in 

 many districts. 



The red deer is still a native of the mountains around the 

 Killarney Lakes, and until recendy a few lingered in the wilds 

 of Connaught, but certainly it is not just now on the Tipperary 

 Mountains, though the fallow deer does occur there. Of the 

 shrews, none of which are given in Mr. Dawkins's list, the pigmy 

 {S. pygmceus) is the only species hitherto identified in Ireland. 

 I mention these facts, having lately bestowed much attention to 

 the study of Irish mammals. A. Leith Adams 



Royal College of Science, Dublin, May 25 



Hints to Workers with the Microscope 



I AM now and have been for the last fortnight enjoying a treat 

 which everyone who possesses a microscope, a slip of glass to lay 

 on the stage, and a piece of thin microscopic glass with a little 

 cottonwool, can enjoy for the price of is. Mr. Bolton, formerly 

 of Stourbridge and now of 17, Ann Street, Birmingham, sends me 

 weekly supplies of rotifers, and has just sent me Rhinops vitraa 

 and Hydatina senta in gi'eat profusion. With ordinary co7n- 

 pressorui and live boxes these are troublesome to see, as they are 

 very lively rovers. To those who may not know the Midland 

 Naturalist or the Microscopic Transactions, I recommend a par- 

 ticular method which I recently sent to those publications. — 

 Take a plane glass slide, on it drop one or more of the rotifers 

 in a drop of water about halfan-inch in diameter, and draw off 

 the surplus water, if any, carefully with the empty pipette. Then 

 fray out a very very small portion of cotton wool (I always use 

 a watchmaker's glass in the eye to do all such operations) until it 

 is much extended, and spread out and lay this on the drop. 

 Upon that lay the thin microscopic glass, the thinner the better, 

 and then set up the capillary attraction by gently touching it m ii h 

 a needle. Draw off any superfluous water from the edges with 

 the pocket-handkerchief and you will have a little wilderness of 

 wool in which the rotifer is restrained in its movements, pro- 

 tected from pressure, and within reach of very high powers. 

 The amount of avooI depends on the size of the rotifer. Hyda 

 tina requires more depth than rhinops. The same plan answers 

 equally well for all roving animals. The poduridas in par- 

 ticular when placed in deep glass cells are easily seen by this 

 apparatus, and it saves many a weary and vexatious five minutes 

 with the compressorium, which, even at the best, requires with 

 living animals extraordinary patience. The rotifers are easily 

 found and secured with the pipette and a watchmaker's glass in 

 the eye after a veiy little practice. Mr. Bolton's studio is of 

 the greatest value to naturalists and cannot be too well known, 

 for to those who have not time to look for specimens it is a 

 great privilege to be able to purchase them. 



Fort Hall, Bridlington Quay, Yorks, F. A. Bedwell 



May 25 



