678 



NA TURE 



[October 31, 1907 



which leads up by easy gradations through both sexes of 

 various species of Perrhybris (another Pierine genus) to 

 the red, black, and yellow Miillerian assemblage we have 

 already considered. From an intermediate stage in this 

 latter series, exemplified on the undersurface of Perrhybris 

 Inrciia J, we get a passage to yet another Heliconiine 

 scheme of coloration, that shown by H. aratica. Here, 

 then, we have groups centring round protected Heliconiines 

 and Ithomiines of the most varied aspects, all held 

 together and linked up with white butterflies of the 

 ordinary Pierine facies by a network of almost imper- 

 ceptible gradations. 



As a final illustration, let me direct your attention to 

 the series formed by Papilio iphidamas 9. Euterpe 

 approximata, E. bcUoiia, E. nigrina (underside), and 

 Hcliiotiitis vetittsta. 



We have only to examine a gradated series like this 

 to see how difficult it is to account for it on Batesian 

 lines. There is the common aposeme, the yellow patch 

 on the dark forewing, running right through ; but if the 

 Papilio is the model for all the rest, why should these 

 Euterpes, which are Pierines, mimic a mimic (the 

 Heliconius) instead of going to the model itself (the 

 Papilio)? If, on the other hand, we regard the Heliconius 

 as the model, we are met by exactly the same difficulty, 

 only that it is reversed. Now' we know that some at least 

 of these intermediate forms are numerous in individuals, 

 and ns soon as the Miillerian principle is admitted wc 

 can see how easily forms protected by distastefulncss can 

 arrange themselves into a gradational series of this kind. 

 For every distasteful form tends to protect other forms 

 on each side of itself ; hence the existence of these 

 transitional stages is just what we should expect. This 

 group represents in miniature what is everywhere to be 

 foimd when w'e examine a tropical butterfly fauna from 

 the point of view of mimicry, and I think we have here 

 discovered the answer to an objection that met us at the 

 outset, namely, the difficulty of accounting, on the prin- 

 ciple of natural selection, for the existence of these inter- 

 mediate forms, including the initial mimetic stages. 

 Whether or no the difficulty is a real one in the way of 

 the Batesian theory, in view of the Mullerian principle it 

 is non-existent. 



The comparison may perhaps be allowed between these 

 mimetic groups, each with its own type of coloration, and 

 the solar and stellar systems. Sometimes, as in the solar 

 system, there is one central member of the group domin- 

 ating the whole and influencing its attendant planets to 

 an extent in comparison with which the force thev them- 

 selves can exercise is insignificant. At other times, as in 

 the systems of double and multiple stars, there are bodies 

 more nearly equal in mass and importance bound together 

 by mutual attraction into a single combination, where 

 each one effectively controls and is controlled by the rest. 

 Could we imagine irregular wanderers through cosmic 

 space which from time to time get drawn within the 

 limits of some established system, we might in them find 

 an analogy to certain species w^hich seem to hover on the 

 outskirts of mimetic groups, undecided, as it were, whether 

 to throw in their lot with one association or another. 



What result have we been able to reach to-night? 

 Starting from the fact, long recognised by naturalists, of 

 the wonderful likeness borne to each other by certain 

 inserts of widely difl'erent afl'mitles, we have found that 

 the first rational explanation of the phenomenon was 

 given by Bates, who nevertheless did not conceal from 

 himself that his interpretation left many of the observed 

 farts unaccounted for. The fertile suggestion of Fritz 

 Miiller went far to supply what was still wanting. 

 Expanded by Meldola and by Poulton, accepted bv 

 travelled naturalists like Wallace and Trimen, the 

 Miillerian generalisation has proved a powerful means of 

 interpretation of many complicated relationships. We 

 have seen reason for concluding that such rival attempts 

 at explanation as those which allege affinity, or geo- 

 graphical and climatic conditions, as adequate' causes" for 

 the phenomena before us, break down on serious examin- 

 ation : and we have applied the final test of arguinff 

 deductively from the premises, and finding, on a fresh 

 apneal to the facts, that our results are in accordance 

 with expectation. 



\0. 1 083, VOL. 76"! 



This verification, we saw, is concerned with the three 

 chief topics of (i^ the interchange of characters, or 

 diaposematism ; (2) the influencing of subordinate members 

 of mimetic groups by one another ; and (3) the nexus 

 of protected conspicuous forms which may overspread a 

 whole zoological continent. 



I think no one who has paid attention to the facts that 

 have been before us can fail to recognise that here, as 

 everywhere in organised nature, the principle of adapt- 

 ation is paramount. No scientific explanation of adapt- 

 ation that really meets the case has yet been offered 

 except natural selection. Whatever bearing the principle 

 of adaptation by selection may have on the question of 

 the origin of species — I for one venture to think that it 

 has a very important bearing — it is a principle which 

 cannot in fairness be ignored. 



In what has been said I have tried to be explanatory 

 rather than controversial, though it has not been possible 

 to avoid altogether points that have given occasion for 

 dispute. Those who are conversant with the subject will 

 know that many questions of interest have been left un- 

 noticed ; but I trust that in this survey, necessarily brief, 

 I have said enough to show how much of biological 

 importance and interest is involved in the reallv great 

 subject of mimicry. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — Mr. R. C. Punnett has been re-elected to 

 the Balfour studentship for one year from Michaelmas, 

 1907. 



A grant of 50I. from the Balfour fund has been made to 

 Mr. W. E. Agar in furtherance of his expedition to the 

 Paraguayan Chaco. 



A proposed change in the Previous Examination, which 

 may be of far-reaching importance, will be voted on by 

 the Senate next week. At the suggestion of the Board 

 of Examinations, a paper on elementary heat and chem- 

 istry will be set in part ii. of the Previous Examination 

 as an alternative to the papers on Paley's " Evidences " 

 and elementary logic. The Board also proposes the sub- 

 stitution of a single combined paper on arithmetic and 

 algebra for the present separate papers on these subjects 

 in the same examination. 



The Special Board for Mathematics has issued an 

 important report with reference to the constitution of the 

 board. _ Owing to the new regulations, the examiners and 

 moderators will in future be nominated by the board. 

 The representatives of the college on the board given 

 them in past years by the nomination of the moderators 

 will thus disappear. The board considers it advisable that 

 there should be direct representation of the mathematical 

 lecturers of the University and of the colleges; it is there- 

 fore suggested that two members be nominated each year 

 at a meeting held of the lecturers in subjects for the 

 mathematical tripos. 



The reforms which the board of mathematics have intro- 

 duced into the University in the last four years are 

 numerous and far-reaching. They include a complete 

 revision of the mathematical tripos, the recognition that 

 the teaching of mathematics should be correlated with 

 that of physics and engineering, the establishment of a 

 qualifying examination in mechanical sciences, re-casting 

 of the mechanical sciences tripos, and reforms in the 

 mathematical special examination for th.-' ordinary degree. 



Dr. Hobson has been re-elected president of the Cam- 

 bridge Philosophical Society. The new vice-presidents are 

 Prof. J. J. Thomson and Mr. S. Ruhemann. The new 

 members of the covmcil are Prof. T. B. Wood, Prof. B. 

 Hopkinson, Dr. Searle, and Mr. W. E. Dickson. Mr. 

 H. F. Newall has been re-elected treasurer, and Mr. .A. E. 

 Shipley, Dr. E. W. Barnes, and Mr. P. V. Bevan 

 secretaries. 



Oxford. — ^The Romanes lecture will be delivered bv the 

 Chancellor of the University, Lord Curzon, All Souls' 

 College, on .Saturday. November 2, at 2.30. In the 

 Sheldonian Theatre. The subject of the lecture will be 

 " Frontiers. ' 



