176 THE LIFE OF A BIRD. 



tiful white ; many eggs, also, are without a second- 



ary colour, but the majority of eggs are ornamented 

 with two or three colours. 



The seat of colour in the eggshell is partly 

 in an external layer of small cells, called the 

 Epithelium, and partly in the deeper layers ; the 

 colouring matter is supposed to be contained, 

 like that of the skin of a negro, in minute cells, 

 which are called pigment cells. It has been found, 

 by chemical experiments upon the beautiful egg 

 of the guillemot, that the colouring matter con- 

 sists, in that case, chiefly of manganese, iron, and 



