Vol. XXXV.] 133 



the species of Geospiza feed, and their bills have become 

 modified to deal with the formidable thorns and spines 

 they encounter. In the desert-regions of Asia and Africa 

 there has developed a whole series of Sand-Grouse (^Ptero- 

 clidce), an order of birds apparently structurally intermediate 

 between the Pigeons and Game-birds, but all showing adap- 

 tation to their desert or steppe environment in the varying 

 shades of yellow and brown of their plumage. 



A great factor in producing colour-changes is the per- 

 centage of damp in the atmosphere and the amount of 

 rainfall. The greater the moisture the darker the coloration 

 becomes, and vice versa. 



It is unfortunate that among birds the effects of environ- 

 ment are not so universally apparent as among insects and 

 other orders of animals ; but it appears to be a common 

 phenomenon that the higher a creature is in the scale, the 

 more difficult it becomes for certain environmental factors 

 to exert their full influence. 



I must apologise for this very short and imperfect pro- 

 duction, but by opening the discussion I hope to create 

 wider interest in the subject. 



Dr. Hartert : I should like to call attention to my old 

 favourites, the Crested Larks. You will see that most of 

 the specimens exhibited have little glass tubes attached to 

 their legs containing samples of the soil on which they 

 were obtained, which illustrates how wonderfully they agree 

 with their surroundings. The North - Algerian Crested 

 Lark [Galerida theklce harterti) is a very dark bird and 

 lives on a very dark soil ; the soil exhibited was taken 

 from the spot where the bird was shot. Then we have 

 the reddish and clay-coloured forms [Galerida theklm 

 hilgerti and G. t. carolince) found on the reddish clay-soil, 

 and, again, the very pale ones (G. theklce deichleri) 

 from the desert-sand. That is all very instructive, and, 

 in the case of these Crested Larks, there is no doubt 

 that it is not the amount of moisture and of rainfall, but 

 actually the general colour of the soil on which they live, 



