288 THE STORY OF THE BIRDS 



oleaginous, whilst in the opposite direction we 

 have the rough-textured eggs of the Grebes 

 and the Cormorants, Gannets, and so forth, 

 the shell of which is coated with chalk, often 

 so thickly as entirely to obliterate the delicate 

 pea-green of the ground colour. The colour 

 of the interior of the shell when held up to 

 the light also presents some diversity, even in 

 obviously very closely allied species. In the 

 Guillemot, for instance, the interior of the shell 

 always appears yellowish-white if held up to 

 the light and viewed through the hole from 

 which the contents have been removed. In 

 the Razorbill, however, the interior of the shell 

 when examined in the same manner is a deli- 

 cate pea-green. This fact always serves to dis- 

 tinguish between the eggs of the two species, 

 even when they closely resemble each other 

 in colour. 



Eggs vary in form almost as much as they 

 do in colour. We do not intend this remark 

 to apply in a strictly individual sense, although 

 considerable variation is apparent in the same 

 species, but chiefly to the various great orders 

 and families. Broadly speaking we can divide 

 their form into three fairly distinct classes or 

 groups, but almost every intermediate shape 



