090 Mr. T. D. A. Cockerel 1 on the 



their species in this condition, .... the proportion of wing- 

 less beetles is larger on the exposed Desertas than in Madeira 

 itself." From these facts he inferred that there had been a 

 survival of the fittest, those forms which were least inclined 

 or able to fly had remained on the islands, while more active 

 iiidividaals had been blown to sea and lost. He also sug- 

 gested that the effects of disuse might have had something 

 to do with the production of wingless species, but this view 

 is now generally discarded, and the case is quoted by authors 

 as one of the best in support of natural selection. 



Although I firmly believe in the potency of natural 

 selection as a directive influence in evolution, I think we 

 must reconsider the case of the Madeira beetles, if only 

 because it is by no means so simple as it first appeared. The 

 facts cited from Wollaston appear striking enough, especially 

 in view of the character of the islands, which are apparently 

 " oceanic," and not remnants of a former extension of the 

 continent of Africa. I have discussed this matter, with 

 special reference to the snails, in 'Nature,' April 8, 1922, 

 p. 446 ; but it is proper to note that Scharfl'C History of the 

 European Fauna,' pp. 19, 25) takes quite a different view. 

 Darwin notes that those Madeira insects which habitually 

 fly are strong-winged (though I should say not exceptionally 

 so), and states that this is not contrary to the view already 

 indicated, for those insects wdiich from their habits were 

 compelled to fly would need to develop powerful wings in 

 order to escape destruction. 



At certain times of the year strong hot winds blow from 

 the African deserts in a westerly direction, and no doubt 

 part of the Madeira insect-fauna has reached the islands on 

 the wing, aided by these powerful currents. Lowe (quoted 

 by Darwin) mentions the arrival on the wing of swarms of 

 locusts in 1844. They were in countless numbers, but after 

 a short time disappeared, '^ and have not since visited the 

 island." However_, they doubtless gained a footing, as 

 Pachytylus dafiicus, L. (which I myself took in Funchal), and 

 Schist ocerca peregrina, Oliv., are at present members of the 

 Madeira fauna — at least the former, and I suppose the latter, 

 a permanent resident. Among the Lepidoptera, Colias edusa, 

 Pyrameis cardui^ Herse convolvuli, Celerio livornica, Macro- 

 glossa stellataruin^ Leucania unipuncta^ Heliothis ohsoleta^ 

 Plusia aurifera^ P. gamma (which has also reached the very 

 isolated Salvages), and others may be supposed to have 

 arrived by flight. I cannot sec, however, that they have in 

 any respect larger or more powerful wings than represen- 



