JuLV 7, 1898J 



NATURE 



223 



department where the complicated subjects bearing on 

 the public health of India can be taught is warmly 

 advocated. 



It was with the idea of securing such means of study 

 that Sir Henry Acland resigned his office into the hands 

 \ of the Regius Professor of Medicine, Prof. Burdon- 

 Sanderson, but, unfortunately, the University is not able 

 to carry out the scheme, and it remains for some wealthy 

 person to grasp the great importance of the various 

 questions involved in the public health of India, and 

 assist the University to provide the means required. 



LETTERS TO THE EDITOR 



{The Ediicr 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 NATURE. 

 No notice is taken of anonymous communications.'^ 



Protective Mimicry. 

 I HAVE read, with special interest, both Sir George Hampson's 

 temarks on certain cases of pseudo-mimicry and Mr. Ed. 

 I'oulton's answer to the same (Nature, vol. Ivii. pp. 364 and 



Now, as I am the person that was consulted on the subject by 

 ■ ne of Sir G. Hampson's correspondents in India, I think my- 

 self entitled, and in a way even bound, as far as possible to 

 remove some of the misgivings that seem to have crept into 

 Mr. Poulton's appreciation as to the true bearing of the facts 

 iiider discussion. 



Though he agrees, on the one hand, with Sir G. Hampson as 



1 the fact that " this and other like cases of mimicry are quite 



destructive of any interpretation of resemblance based on 



liates' theory," he yet maintains, on the other, that '* they do 



not similarly affect the Miillerian theory." 



But this is precisely what I contend is contradicted by the 

 facts in question. To make this clear, I shall only use Mr. 

 Poulton's own statements and admissions. 



" The MuUerian theory," he says, " supposes that a common 

 type of appearance among distasteful insects in the same 

 locality acts as a common advertisement to enemies, so that the 

 loss of Ufe which must ensue during the time in which each 

 generation of enemies is being educated to avoid the owners 

 if a particular type or pattern and colouring is shared between 

 he species instead of being borne by each independently." 



The theory, thus understood, seems to Mr. Poulton to be 

 rather exemplified and confirmed than contradicted by the facts 

 in question, and he therefore continues : " It is probable that 

 Tercuoli are on the whole avoided by birds ; and if this is also 

 true of the Abraxas, the resemblance may well be advantageous, 

 in spite of the difference in station, even granting that the 

 ' good round sum ' of 6000 feet is an absolute barrier to the 

 Teracoli below and the Abraxas above. But future investigation 

 may show that they approach much nearer than this." 



First of all this reasoning, which is openly all about admitted 

 icts, looks rather as a running away from those facts to some 

 wished-for possibilities. Besides Mr. Poulton grants, after all, 

 that unless both types occur in the same locality and be exposed 

 to the same enemies, no possible training of young birds can be 

 conceived, and consequently no ad%antage can be supposed to 

 accrue. 



But what are the facts ? For here, of course, I do not pre- 

 tend to discuss what might take place in any possible sup- 

 position, nor even to find fault with the logical slip so very 

 common among natural selection evolutionists, which consists 

 in so confounding the simple admission that similarity of 

 colour exists, or even is useful, as to conclude from it that it is 

 therefore the result of usefulness. 



Now, so long as we keep to facts, whether we consider the 

 two species of butterflies themselves or their respective enemies, 

 the conclusion is the same, and they both require distinct 

 climatic conditions and distinct " habitats." 



Willingly or not, we must resign ourselves to see the "good 

 round sum" of 6000 feet, or rather the difference in climatic 

 conditions and other "surroundings" represented by this dif- 

 ference in elevation in our regions of Southern India remain as 

 an insuperable barrier between the above-named species of 

 Ibutterflies, and to much the same extent also between their 

 enemies. 



Far from coming into contact, therefore, they are thus kept 

 by their habits apart from one another, and put under con- 

 ditions quite different from those required for the possible 

 application of even the Miillerian theory. 



Finally, both from the evidence of these and many like facts 

 and, as Mr. Plateau has so well demonstrated, from the trifling 

 importance of colouring in the selection of insects by their 

 enemies, it is, to say the least, difficult to see how the facts of 

 similarity in colour, shape, &c. — which for shortness sake we may 

 even call "mimicry" — can be interpreted or explained by any 

 possible theory based on simple natural selection. And I would, 

 m conclusion, reniark that I distrust all such theories not, as 

 Mr. Poulton seems to believe, "on the ground that the evidence 

 is not demonstrative," but because, far from offering an intelli- 

 gible and possible explanation of facts, they simply stand in 

 contradiction with them and mislead us as to their real meaning. 



J. Castets, S.J. 



St. Joseph's College, Trichinopoly, India, June 8. 



I DO not propose to deal with Mr. Castets' objections to 

 natural selection in general. They have often been met before. 

 As to the special case under discussion, he feels that his know- 

 ledge of the distribution of the two species is exhaustive enough 

 .to give him safe warrant for the assertion that they are invariably 

 separated by a height of 6000 feet. If this conclusion is well 

 founded, it is an important contribution to the facts of the case 

 under discussion. Nevertheless neither this nor the climatic 

 differences need affect the Miillerian theory if the barrier which 

 separates the one form from the other is crossed by the enemies 

 of both. The Teracolus-XiV^ appearance of the moth is remark- 

 able, and separates it very sharply from its allies. It occurs on 

 an elevated district surrounded by lower country in which the 

 Teracolus abounds. The approximation is sufficient to render 

 the Miillerian theory a probable explanation in view of the im- 

 mense number of similar relationships accompanying a closer 

 approximation in other parts of the world, and considering the 

 complete absence of any other explanation ; unless, indeed, 

 Mr. Castets intends to imply, by so constantly dwelling upon 

 one aspect of the environment, that the difference in climate is 

 responsible for the agreement in appearance. 



Oxford, June 30. E. B. Poulton. 



Epidemics among Mice. 



Referring to a paragraph in your issue of June 23 (p. 179), 

 relative to the discovery by Dr. Issatschenko of a new microbe 

 pathogenic to rats, I would call attention to some articles by 

 Prof. F. Loetfler on epidemics among mice, (S:c., in the Central- 

 blatt fiir Bacteriologie imd Parasitenkunde, Band xi. pp. 129- 

 141 (February 10, 1892), and Band xii. pp. 1-17 (July 5, 1892), 

 which will be found translated in a Blue Book entitled, " Report 

 of the Departmental Committee appointed by the Board of 

 Agriculture to inquire into a Plague of Field-Voles in Scotland, 

 with Minutes of Evidence and Appendices and a copy of the 

 Minute appointing the Committee" (1893). Translations of 

 the above papers form Appendix vi. of this Report ; and Prof. 

 Loeffler's second paper relates his successful efforts to employ 

 the " Bacillus typhi murium" to destroy field-voles in Thessaly. 



It would be interesting to know whether the microbe dis- 

 covered by Dr. Issatschenko is the same as that described by 

 Prof. Loeffler, or a different species. W. F. KlRBY. 



Chiswick, June 25. 



Remarkable Hailstones. 



On Sunday, June 26, a district to the south of Manchester 

 was visited by a thunderstorm, which was remarkable for its 

 accompaniment of heavy hail. The storm came from the same 

 quarter as the cool surface wind, viz, north-east, and reached its 

 height about 2.15 p.m. 



Preceded by a lull in the heavy rain, hail, accompanied by 

 lightning, began to fall, and continued to do so for five minutes. 



The most noticeable fact was the peculiar shape of the hail- 

 stones. The.se were conical in shape, about i inch long, and § 

 broad in widest part. In longitudinal section they showed 

 (a) opaque white bands ; {b) clear, colourless bands ; {c) semi- 

 opaque bands, dotted with more opaque portions. 



All of those examined agreed in possessing transparent 

 portions at the vertex and base. On making a transverse 

 section through one of the opaque bands, it was seen to consist 

 of (a) narrow clear channels intersecting the surface ; {b) opaque 



NO. 1497, VOL. 58] 



