OVIPAROUS ANIMALS. 414 
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- 
laze 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 halones. 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 contamed, analogeus 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 
VOL. I. pd 
