THE EGG OF BIRDS. 39 



what it is desirable to see, the gash should be only sufficient to 

 give a directing tendency, which may be followed up by care- 

 fully pulling apart the yolk with the fingers. The structure of 

 the interior will explain for itself why the yolk splits more 

 readily through the white spot than at right angles to that axis. 

 It is impossible, even with the most prolonged boiling, or immer- 

 sion in spirits, to harden that part of the yolk which extends 

 from the white spot (cicatricula) (c) to the centre (v) of the 

 spheroid, and consequently there is the least cohesion along that 

 line, and therefore the split takes place most readily in that 

 direction. These same peculiarities, which I have and am 

 about to describe, exist in the egg just before the white and the 

 shell are deposited around it, but the characters are not quite so 

 strongly marked as in the laid egg; and for this reason I have 

 chosen the latter for the better purposes of demonstration, and 

 that you may repeat the observation for yourselves. The prin- 

 cipal feature, to which I wish to draw your attention, is the 

 arrangement of the yolk in concentric layers (o?), which are 

 alternately dark and light, from the centre to the circumference. 

 These layers, as you will observe, do not form perfectly closed 

 circles, but on the side next the cicatricula bend outwardly and 

 terminate at the circumference. They might be compared to a 

 set of vases placed one within the other, the central one (v, v 1 } 

 containing the uncoagulated fluid which extends from the cica- 

 tricula (c) to the centre. In the egg, before it has the shell and 

 white deposited around it, the germinal vesicle would then be 

 found just at the mouth of the central vase (v, v 1 ) ; but at this 

 stage there is a mere trace of it, in the form of a clear area (p) 

 just beneath the cicatricula (c). In specimens of birds' eggs, 

 preserved in spirits, the more highly oleaginous nature of the 

 darker layers is particularly well demonstrated, as the latter 

 assume in that condition a dark orange hue, and the oil oozes 

 out in large quantities at the surface of the fissure, and floats off 

 in drops. 



The popular idea of an egg includes the " white," which is 

 merely an accessory, like the shell, and really has no direct 



