NA TURE 



[November 25, 1909 



sarily meagre, whereas such matter as a list of photo- 

 graphic chemicals required, with the prices — informa- 

 tion that can be obtained from any trade catalogue — 

 might easily have been omitted. On the whole, how- 

 ever, the object of the book is fulfilled, and it will 

 form, to those who have a microscope of simple con- 

 struction, or who, having a camera, wish to apply 

 it for microscopic work as well, a most useful guide. 

 The illustrations are in all cases of a high order, and 

 have been selected, not merely as pictorial examples 

 of photo-micrographic work, but, so far as possible, to 

 bring home to the student the difficulties to be 

 encountered and the results to be attained. 



J. E. Barnard. 



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 intended for tliis or any other pari o/ Nature. 

 No notice is taken of anonyynous communications.] 



The Inheritance of Acquired Characters. 



In reviewing Prof. Eigenmann's book on the cave verte- 

 brates of America (Nature, November ii, p. 40), the re- 

 viewer quotes the author's opinion that " The bleached con- 

 dition of animals living in the dark, an individual environ- 

 mental adaptation, is transmissible, and finally becomes 

 hereditarily fi.xed. . . . Natural selection cannot have 

 affected the coloration of the cave forms, for it can be of 

 no consequence whether a cave species is white or black." 

 Your reviewer further dismisses Romanes's supposition that 

 colour may be correlated with other structures which are 

 subject to selection. 



Is it not probable that the mere cessation of natural 

 selection with regard to colour would produce this colour- 

 less condition quite apart from light or other environmental 

 factor ? 



In the silkworm'moth, Bomhyx mori, we have a similar 

 absence of colour in both moth and larva, solely, I take 

 it, because no attention has been paid to the colour 

 of either during the many centuries that the species has been 

 selected for its silk-producing qualities alone under semi- 

 domestication. 



While on this subject, I may perhaps refer to Mr. Wm. 

 Wood Smyth's letter in Nature of May 6 last (vol. 

 Ixxx., No. 2062, p. 277), with reference to the drone breed- 

 ing habits of some workers of the hive bee affording a 

 possible channel for use inheritance in regard to neuter 

 characters. 



I had hoped that this important point would have been 

 the subject of further correspondence by the acknowledged 

 authorities on apiculture. 



I thought that this feature of egg-laying workers was, as 

 .T rule, confined to queenless hives that were more or less 

 in extremis. Presumably the habit would be subject to 

 heredity, and if, as I understand, it is not only a detriment 

 but a source of danger to any community of bees to have 

 any number of egg-laying workers, it seems reasonable to 

 suppose that in wild stocks such a habit would be so 

 stringently restricted by natural selection as to deprive its 

 occasional occurrence in domesticated stocks of any sig- 

 nificance in the production of the structural differences or 

 special habits which differentiate workers from queens. It 

 would be of very great interest to know if neuter ants of 

 any species retain the power of laying; occasional eggs. 



A. Bacot. 



Mr. Bacot's suggestion with regard to the cessation of 

 natural selection in relation to the bleaching of cave animals 

 has been fully dealt with by Prof. Eigenmann himself in the 

 work under review. It will be only fair to Prof. Eigen- 

 mann to quote his own words :— " Panmixia can not 

 account for the discharge of the colour, since it returns in 

 some species when they are exposed to the light and dis- 

 appears to a certain extent in others when kept in the dark. 

 NO. 2091, VOL. 82] 



Panmixia, Romanes thinks, may have helped to discharge 

 the colour. In many instances the colour is a protective 

 adaptation, and therefore maintained by selection. Panmixia 

 might in such instances lower the general average to what 

 has been termed the 'birth-mean.' Proteus is perhaps 

 such an instance. But in this species the bleached condition 

 has not yet been hereditarily established, and since each 

 individual is independently affected, ' the main cause of 

 change must have been of that direct order which we 

 understand by the term climatic' Since, however, the 

 bleached condition, which in the first instance is an indi- 

 vidual reaction to the absence of light, has become heredi- 

 tarily established in Amblyopsis so that the bleaching goes 

 on even when the young are reared in the light, it is 

 evident that in Amblyopsis we have the direct effect of 

 the environment on the individual hereditarily established." 

 If Mr. Bacot will read the notice again he will see that 

 the reference to " Romanes's supposition that colour may 

 be correlated with other structures which are subject to 

 selection " is a quotation. The reviewer still considers, 

 however, that Prof. Eigenmann has made out a strong 

 case. Arthvr Dendv. 



Radio-activity and the Rocks, 



Mr. F. p. Mennell. in N.\ture of November 18, 

 raises the question whether the more strongly active of 

 the rock-forming minerals owe their activity to thorium. 

 I have a considerable number of data on this subject 

 obtained by direct experiment, estimating radium and 

 thorium by their eman;,-;ions. I find, by this method, that 

 zircon, sphene, and apatite usually contain some thorium, 

 but that it generally contributes less to the activity than 

 the substances of the uranium-radium series. 



R. J. Strutt. 



Imperial College of Science, South Kensington, 

 November 20. 



The Auroral Display of October 18. 



The aurora of October iS was observed at Allegheny 

 Observatory under conditions somewhat similar to those 

 mentioned by Mr. Ernest Baty in Nature of October 28 

 (vol. Ixxxi., p. 518). Here, however, the whole sky was 

 dull, hazy, and cloudy at the beginning of the display, 

 gradually clearing toward midnight. No stars whatever 

 could be seen in the region covered by the aurora, which 

 was very bright. This fact might lead us to think that it 

 had its origin in the lower layers of the atmosphere. 



The aurora consisted of the usual arch, from which arose 

 streamers at various points, some of them extending to an 

 altitude of about 45°. These drifted westward and 

 gradually diminished in brightness, while they were 

 followed by others in rapid succession. The streamers had 

 at times a reddish tint. 



The aurora was still faintly visible at i a.m., by which 

 time the sky had become perfectly clear. 



F. C. JOROAN. 



Allegheny Observatory, Allegheny, Pa., 

 November 9. 



Large Flying-fish. 



A FLVING-FISH flew on to the lower deck last night 

 about 8.30 p.m. The deck is 20 feet above the water- 

 line, and the railing is 4 feet 6 inches above the deck, but 

 it is possible for it to have flown through the railing; the 

 fish measured 17^ inches from tip of nose to tip of tail. 

 I forgot to weigh it before It was cooked. It was the 

 largest fiying-fish I have ever handled. Could any reader 

 of Nature kindly inform me what is the largest size 

 known? We were about fifty miles north of Teneriffe 

 when it came on board. The species up here appear to be 

 larger than those in the tropics and near South America. 

 I have seen large ones in the Gulf of Aden, but never 

 caught one, though I am inclined to think this was a larger 

 species. The longest flyers always appear to be the largest 

 fish ; the longest flight I have seen has been about 400 

 yards. C. Howard Tripp. 



.S.S. Kaipara, October 15. 



