PROTECTIVE RESEMBLANCES IN VERTEBRATA 61 



they undertake the duties of incubation. The same 

 necessity does not apply to species which construct 

 covered nests or build in holes. 



The Colours and Markings of Birds' Eggs 



The protective value of the tints and markings 

 of eggs are of great interest, and have not been 

 sufficiently investigated. The fact that eggs are 

 protectively coloured was fully recognised by Erasmus 

 Darwin, who places them under ' colours adapted to 

 the purpose of concealment.' He says ' the eggs of 

 birds are so coloured as to resemble the colour of 

 the adjacent objects and their interstices. The eggs 

 of hedge-birds are greenish with dark spots; those 

 of crows and magpies, which are seen from beneath 

 through wicker nests, are white with dark spots ; and 

 those of larks and partridges are russet or brown, like 

 their nests or situations.' ^ This description of the 

 eggs of crows and magpies is incorrect. The eggs 

 of crows are greenish with umber markings ; those 

 of magpies pale greenish with dark markings. It is 

 probable that Erasmus Darwin correctly explained 

 the appearance of the eggs of the wood-pigeon (see 

 p. 62), and inadvertently illustrated this principle of 

 colouring by erroneous instances. The special men- 

 tion of the interstices between the parts of sur- 

 rounding objects, as well as the objects themselves, is 



• Zoonomia, 1794, vol. i. p. 510. 



