120 HABITS OP BIRDS. 



bright pale blue of those of the redstart and the 

 hedge-sparrow (Accentor modularis), must be pro- 

 duced, like the black bones in the fowls of Malabar, 

 by a uniform colouring matter in the calcareous se- 

 cretion; and we accordingly find, that when subjected 

 to the action of dilute hydrochloric acid, the whole shell 

 of an egg, uniformly coloured, becomes dissolved, the 

 dissolution being as perfect in the instance of the blue 

 egg of the hedge-sparrow and the green egg of the 

 nightingale as in the ivory-white egg of the wood- 

 pecker. A similar experiment upon any uniformly- 

 coloured shell, such as the common pale yellow snail- 

 shell (Helix hortensis) is attended with nearly the 

 same result, a thin membranous pellicle only re- 

 maining undissolved by the acid. But when the 

 banded snail-shell (H. nemoralis) is subjected to the 

 acid, the coloured bands having less calcareous and 

 more animal matter, remain in a loosened and some- 

 what flocculent form, but considerably thicker than 

 the portion where the ground colour prevails, proving 

 that the bands consist chiefly of animal matter. On 

 examining the mantle of the snail from which the 

 shell is secreted, we find that it is marked with dark 

 translucent bands, exactly correspondent to the bands 

 on the shell ; and it may be that these bands, being 

 less brittle than the other portions of the shell, are 

 intended to strengthen its texture. 



The various markings on the eggs of many species 

 of birds are, in all probability, formed in a similar 

 manner to the bands on snail- shells, namely, by 

 glands secreting colouring matter, distributed amongst 

 those which secrete the general ground colour or the 

 uncoloured portions. From the formation of the egg- 

 shell, however, taking place within the egg-tube, it is 

 out of the reach of observation, while the process of 

 forming the snail-shell can be seen at every step. 

 This probability is strengthened by the similar effect 



