NATURE 



[October i, 1891 



crops. Thus, potassium chloride replaces potassium 

 nitrate in the manure for leguminous plants, and in 

 some cases a mixture of potassium chloride and am- 

 monium sulphate replaces potassium nitrate ; and a 

 few other alterations are suggested in the treatment of 

 various crops. Thomas's basic cinder is not mentioned 

 as a source of phosphoric acid. The lectures themselves, 

 and some contioversial matter, are reprinted in their 

 original form, and but little new matter is added. 



LETTERS TO THE EDITOR. 



{The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of ^ATVK%. 

 No notice is taken of anonymous communications. '\ 



The Bird-Collections in the Oxford University 

 Museum. 



DUKING a recent visit to Oxford I took the opportunity of 

 examining the collection of birds in the University Museum, 

 and beg leave to offer a few remarks upon its condition. 



First, as regards the mounted specimens, there are three series 

 belonging to this category : — 



(i) The general series in the Central Court, This numbers 

 about 1 100 specimens, which are contained in twelve cases, 

 placed in opposite rows of six each, but rather mixed up with 

 mammals, shells, and other objects. The specimens are 

 arranged according to Gray's "Genera," and in most cases 

 correctly named. But many of them are in bad order and 

 not well set up, and should be replaced by fresh examples. 

 The whole series requires renovation and rearrangement, ac- 

 cording to some modern system, and the orders and families 

 should be designated by labels, and distinctly separated one 

 from another. 



(2) The collection of Arctic birds formed by Mr. J. Barrow, 

 F.R.S., and presented to the Museum by that gentleman. This 

 interesting collection, which has been well described by Mr. 

 Harting in the Ibis, is placed in the gallery. It is well 

 mounted and correctly named. But it is a question whether it is 

 desirable to keep it apart from the general series. 



(3) The British series, also placed in the gallery, which is in 

 fair order, although it also requires revision and rearrangement 

 according to some modern system. It ought not to be difficult 

 to find some member of the British Ornithologists' Union to 

 undertake this task, provided that the authorities will allow him 

 a " free hand." 



Besides the mounted specimens, there are, as I understand, 

 about 4000 skins of birds, most of which are " put away " in 

 boxes in various parts of the building. Of these, the only portion 

 that I was able to see was the Bornean collection formed by 

 Mr. Everett, and partly described by Dr. Bowdler Sharpe 

 in the Zoological Society's Proceedings. These are placed 

 in some drawers in the main hall. The other skins are 

 stated to be "boxed up," and are kept partly in a room on 

 the ground floor, and partly in some "upper chamber," to 

 which no ready access is possible. 



I venture to suggest that one of the side rooms in the 

 Museum should be cleared of its contents, and devoted en- 

 tirely to the bird-skins, and that they should be arranged there 

 in cabinets, so as to be accessible to the ornithologist. It is 

 hardly right for a great and rich University to accept collections 

 from persons who, in the words of the lale Prince Bonaparte 

 put forward on a similar occasion, "croyant qu'ils travaillaient 

 pour la science, non pas travailles que pour les mites." I may 

 add that any assistance that I can give in carrying out this 

 reform will be most gladly rendered. P. L. Sclater. 



3 Hanover Square, London, VV., September 4. 



Variation and Natural Selection. 



In Prof. C. Lloyd Morgan's Presidential address to the 

 Bristol Naturalists' Society, on "The Nature and Origin of 

 Variations " (of which he has kindly sent me a reprint from the 

 Society's Proceedings), there are one or two points on which 

 there seems to me to be a slight misconception ; and as the 

 difficulties suggested have probably occurred to other naturalists. 



I wish to make a few observations in the hope of throwing a 

 little light on this obscure subject. 



After referring to the proofs of the variability of species in a 

 state of nature which I have adduced in my " Darwinism " (to 

 which proofs Prof. Lloyd Morgan has made some important 

 additions in his recent work on " Animal Life and Intelligence") 

 he remarks : — "We have been apt to suppose that a species is so 

 nicely adjusted to its surrounding conditions that all variations 

 from the type, unless of a very insignificant character, would be 

 rapidly and inevitably weeded out. This, it is clear, is not true 

 at any rate for some species." And a little further on, after dis- 

 cussing the question whether variations in all directions occur in 

 equal proportions — an equality which does not appear to me to 

 be at all necessary, or to have been ever suggested as occurring 

 — he says: "And the candid biologist must, I think, admit 

 that the evidence in Mr. Wallace's third chapter, while con- 

 clusive as to the occurrence of variations, gives on analysis little 

 or no evidence of any selective agency at v\ork." 



The difficulties here staled appear to me to depend, chiefly, 

 on not taking account of some important facts in nature. The first 

 fact is, that the struggle for existence is intermittent in character, 

 and only reaches a maximum at considerable intervals, which 

 may be measured by tens of years or by centuries. The average 

 number of the individuals of any species which reach maturity 

 may be able to survive for some years in ordinary seasons or under 

 ordinary attacks of enemies, but when exceptional periods of 

 cold or drought or wet occur, with a corresponding scarcity of 

 certain kinds of food, or greater persecution from certain 

 enemies, then a rigid selection comes into play, and all those in- 

 dividuals which vary too far from the mean standard of efficiency 

 are destroyed. 



Another important consideration is that these epochs of severe 

 struggle will not be all of a like nature, and thus only one par- 

 ticular kind of unbalanced or injurious variation may be 

 eliminated by each of them. Hence it may be that for consider- 

 able periods almost all the individuals that reach maturity may 

 be able to survive, even though they exhibit large variations in 

 many directions from the central type of the species. During such 

 quiescent periods, the chief elimination will be among the young 

 and immature. Thus, with birds probably nine-tenths of the 

 destruction occurs among the eggs and half-fledged young, or 

 among those which have just escaped from parental care ; while 

 those which have survived to breeding age only suffer a slight 

 destruction in ordinary years, and this may occur partly among 

 the less experienced, partly au.ong those which are old and 

 somewhat feeble. 



The severe elimination that occurs in the earlier stages may be 

 thought to be accidental, but I doubt if it is really so except in 

 a very small degree. The protection and concealment of the 

 eggs and young in the nest will depend chiefly on the mental 

 qualities or instincts of the parents, and these will have been 

 always subject to a rigid selection owing to the fact that those 

 with deficient instincts will leave fewer offspring to inherit their 

 deficiency. And with yourg birds of the first year there will be 

 an equally rigid selection of the incautious, and of those who are 

 deficient in any of the sense-perceptions, or are less strong and 

 active than their fellows. 



The proof that there is a selective agency at work is, I think, 

 to be found in the general stability of species during the period 

 of human observation, notwithstanding the large amount of 

 variability that has been proved to exist. If there were no 

 selection constantly going on, why should it happen that the 

 kind of variations that occur so frequently under domestication 

 never maintain themselves in a state of nature ? Examples of 

 this class are white blackbirds or pigeons, black sheep, and 

 unsymmetrically marked animals generally. These occur not 

 unfrequently, as well as such sports as six-toed or stump-tailed 

 cats, and they all persist and even increase under domestication, 

 but never in a state of nature ; and there seems no reason for 

 this but that in the latter case they are quickly eliminated through 

 the struggle for existence— that is, by natural selection. 



One more point I will advert to is Prof. Lloyd Morgan's 

 doubt, in opposition to Mr. Ball, " whether a thicker or thinner 

 sole to the foot is a character of elimination value, whether it 

 would determine survival or elimination, and make all the 

 difference between passing or being plucked in life's great com- 

 petitive examination." This seems to me to be a rather unfor- 

 tunate objection, since, in constantly recurring circumstances 

 during the life of a savage, this very character must be of vital 

 importance. Whether on the war-path, or in pursuit of game, 



NO. II 44, VOL. 44] 



