OVIPAROUS ANIMALS. 417 



yolk-bag. From each end of the yolk proceeds a white 

 knotty body, which terminates in the glaire by a white floc- 

 culent extremity. These knotty bodies are called the cha- 

 laza. or grandines. What is termed the cicatricula, or tread 

 of the cock, is a round milk-white spot, formed after im- 

 pregnation, on the surface of the yolk-bag, and surrounded 

 with whitish concentric circles, termed Jialones. The glaire 

 contains chiefly albumen and water, and the yolk has, in 

 addition, a portion of oil, to which it owes its yellow colour. 



The glaire and the yolk are common to all eggs, differ- 

 ing greatly, however, in many of their characters. Where 

 the egg is destined to be hatched in water, the glaire is a 

 substance intermediate between gelatine and albumen, and 

 capable of resisting the macerating effects of the surround- 

 ing fluid. The yolk is sometimes single, as in the eggs of 

 insects, or compound, producing in one egg many young, 

 as in some species of leeches. The membrana albuminis is 

 present in many eggs, while, in several cases, the glaire of 

 many yolks is united to form a connected mass. 



In birds, the ovarium appears like a bunch of grapes, 

 consisting of the bags containing the yolks, with their stalks 

 of attachment. When the yolk has attained its full size, 

 the bag or calyx in which it is contained, analogous to a 

 corpus luteum, exhibits a white shining line, marking the 

 intended opening, which at length takes place, and suffers 

 the yolk to escape into the expanded extremity of the ovi- 

 duct. The calyx is by degrees absorbed, and in old age 

 nearly disappears. The yolk, in passing along the oviduct, 

 acquires the glaire, and likewise the shell, and becomes fit 

 for exclusion. 



The manner in which the eggs of birds are impregnated 

 by the male has not been satisfactorily determined. With 

 the exception of the cicatricula, a bird, in the absence of a 



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