INTRODUCTION. 11 



of the feathers, &c. have any thing to do in con- 

 centrating- the heat, or that black might conduct 

 the heat through the nest by radiation, and thus 

 allow it to escape, we cannot say; but we can 

 vouch for the fact, — ^that the feathers and hair, 

 found in the insides of the nests of birds, are al- 

 ways white, grey, or light-coloured. 



The materials employed by bii'ds, in forming 

 their nests, are, perhaps, better criterions to judge 

 of the species by, than even the colom's of the eggs, 

 \\ hich, in very different genera, as well as in dis- 

 tinct species, are often very similar in tint ; while, 

 amongst the eggs of the same species, a consider- 

 able difference may be found with regard to the 

 coloiu- of their spots or freckles. The colour of and 

 the freckles on eggs appear to us to be produced 

 much in the same manner as the tints and spots 

 on the shells of snails ; that is, — ^we conceive the 

 colouring matter is forced through the shell by 

 some process unknown to us, from the inner to 

 the outer surface, where it appears brightest ; but 

 with this difference, — ^that the colours of the eggs 

 of a bird bear no analog}^ to that of the matter un- 

 der the shells, or to the feathers of the parent- 

 bird; whereas many testaceous animals, — such as 

 snails, — ai-e found to be marked with colours si- 



