164 Wonders of the Bird World 



feature not entirely confined to these birds, as the Guira 

 Cuckoo of South America lays a blue egg which is almost 

 entirely hidden by the chalk which overlays it. Some 

 Storks also have a chalky egg. With regard to the ap- 

 pearance of the eggs of the Geese and Ducks there is much 

 sameness, and the principal peculiarity connected with their 

 breeding habits is the lining of the nest with down from 

 the body of the female bird; and so characteristic is this 

 down, that, in the majority of cases, the eggs of the different 

 species of Ducks can be determined by the colour of the 

 down which lines the nest. 



In the descriptions of the eggs given above in my 

 short review of the Families of Birds, it will be 'noticed 

 that I occasionally speak of some of them as " double- 

 spotted." This is one of the most important features in 

 the study of Oology, and relates to the prominence of the 

 underlying spots and markings (generally grey or purplish), 

 which, in those eggs wherein they are a feature, are some- 

 times as much in evidence as the overlying or darker 

 markings of the shell. Thus, for instance, on the strength 

 of the eggs alone, one can separate the Herons from the 

 Cranes, though in olden times they were always classified 

 together, for the former birds lay an unspotted blue or 

 whitish egg, whereas in the Cranes the egg is always dark 

 and "double-spotted." In most of the Passeriformes or 

 Perching-birds it will be also noticed that where the eggs 

 are spotted the markings are of this two-fold nature. 



Plovers and Snipes lay characteristic eggs, and in nearly 

 every case the latter are pear-shaped, four in number, and 

 are placed point to point, and in this group of birds 

 Oology is of great service in classification, as the eggs 

 laid by the Crab-Plovers, Coursers, Pratincoles, Jacanas, 

 Plovers, and Bustards are of such a different type from 

 those of the true Plovers, that it would be impossible on 

 this account alone to place them in the same Sub-Order, 



