Vol. XXXV.] 130 



into screw-paddles for rapid swimming ; while in the 

 sea-snakes the tail has been transformed for a similar 

 purpose. 



Among the many phenomena connected with evolution 

 none have aroused greater interest than so-called '^ Mimicry" 

 and "Protective Resemblance/' and these call for special 

 attention at the present moment, since they are denied by 

 the extreme " Mendelians." 



Even before this attitude of the " Mendelians " a number 

 of biologists adopted a hostile attitude to " Mimicry," owing 

 to the extravagant assertions made by many of its sup- 

 porters. Some of them went so far as to say that the 

 variation necessary to bring about " Mimicry " and " Pro- 

 tective Resemblance " was to a great extent voluntary on 

 the part of the organisms involved. This, of course, is pure 

 imagination. In our own branch of ornithology, we have 

 an almost negligible number of instances which can be 

 brought under the heading of " Mimicry " — in fact, the only 

 ones generally quoted are certain Cuckoos and the genus 

 Buchanffa, the Moluccan and Papuan " Dusky Orioles," and 

 the Honey-eaters called " Friar-Birds.'^ The Cuckoos are 

 apparently very evident cases of " Mimicry " for agressive 

 purposes ; but the object of the resemblance between the 

 Dusky Orioles and Friar-Birds is far from clear. 



On the other hand, cases of "Protective Resemblance" 

 among birds are numerous, and certainly show clearly the 

 effects of environment. In desert-regions the large majority 

 of the birds are sand-coloured or else black ; the latter so 

 that they may be hidden in the shadows thrown by rocks 

 and stones. 



The evolutionary process due to environment is clearly 

 shown in the Crested Larks of Algeria. In the desert these 

 are sand-coloured, while in the north they are dark, ex- 

 hibiting various shades of brown, similar to the rich soil 

 upon which they live. In the central plateau they are 

 brownish-grey, like the mixed soil, and in the extreme 

 south they are yellow, like the' rocky patches amongst the 

 sand and clav. 



