Ornithology. 77 



there are probably very few instances of such productions 

 from birds in their wild state, yet it is no uncommon thing in 

 domestic fowls. 



We are also told of eggs with double shells ; and we fre- 

 quently see eggs without any calcareous covering, but wrapped 

 in a soft pliable skin like vellum. 



To account for these extraordinary productions, we must 

 conceive a defect exists at the time in some part of the 

 animal body ; and as the vitellus and albumen derive their 

 origin from different parts, it is natural to conclude, in those 

 preternatural eggs destitute of yolk, the cause proceeds from 

 some defect in the ovarium. May it not be occasioned by 

 an unequal stimulus in the parts necessary to perfect the egg, 

 and that the growth of the vitellus is not in proportion to the 

 albumen^ Thus while the vesicles appointed for collecting, 

 preparing and uniting the organic particles of the albumen in 

 the uterush^.\e all their effective powers, those of the ovarium 

 are weak ; of course the one goes on with the operations 

 appointed by nature, while the other is stopped in its progress 

 for want of a sufficient quantity of organic matter to bring it 

 to perfection at the same time. Hence the reason of the 

 common fowls sometimes producing three or four imperfect 

 eggs following, by which the vitellus becomes sufficiently 

 large, and a regular succession of perfect eggs are produced. 

 On the contrary, when, from the same causes, the growth of 

 the vitellus in the ovarium is too luxuriant, two yolks pass the 

 oviduct together, which being surrounded with the usual 

 quantity of the albumen, is brought forth in the form of a 

 single egg of an extraordinary size. From these it is possible 

 that twins are produced, but more frequently deformities, 

 which are seldom hatched. 



Color of Eggs. It was a notion of Darwin's that the 

 variety in the colors of eggs, as well as in the colors of many 

 animals, is adapted to the purposes of concealment from their 

 natural enemies. Thus, he remarks that the eggs of the 

 hedge chanter are greenish blue, as are those of crows, which 

 are seen from beneath in wicker nests, between the eye and 

 the blue of the firmament. M. Gloger, a German naturalist, 

 has followed up this singular theory into some detail, and 

 considers it to be a remarkable provision of nature, that birds 

 whose nests are most exposed, and whose eggs are most open 

 to the view of their enemies, lay eggs of which the color is 

 the least distinguishable from that of surrounding objects, so 

 as to deceive the eye of birds, or of other plundering animals; 

 while birds, the eggs of which have a bright decided color, 



