212 THE COLOURS OF ANIMALS 



when the annual is already alarmed and in full retreat 

 for a place of security. 



In this way Mr. Wallace explains the conspicuous 

 markings often present on gregarious ruminants, 

 which are nevertheless protectively coloured in other 

 respects. The remarkable differences in the length 

 and form of the horns of different species are explained 

 in a similar manner. 



Eecognition Markings in Birds 



Mr. Wallace also shows that such characters are 

 especially numerous and suggestive among birds. 

 ' Eecognition Marks during flight a,re very important 

 for all birds which congregate in flocks or which 

 migrate together ; and it is essential that, while being 

 as conspicuous as possible, the marks shall not inter- 

 fere with the general protective tints of the species 

 when at rest. Hence they usually consist of well- 

 contrasted markings on the wings and tail, which are 

 concealed during repose, but become fully visible 

 when the bird takes flight ' {he. cit. p. 222). 



Recognition of Birds' eggs may be aided by variation 

 in certain species 



It is very probable that the great variation in the 

 colours and markings of birds' eggs, which are laid 

 close together in immense numbers, may possess this 



