29G 



EMBRYOLOGY. 



lamina being entitled the serous or animal layer, the inferior 

 the mucous or vegetative layer ; the former is limited to the 

 extent of the area pellucida, the latter extends farther in the 

 periphery, stretching beyond the area vasculosa. The albu- 

 men disappears in a great measure over the germinal mem- 

 brane, and the vitellus approaches the lining tunic of the shell 

 more closely ; in this situation, the vitellus becomes more pro- 

 minent, forming a segment of a lesser sphere, like the cornea 

 of the eye ; a circumstance which may likewise be frequently 

 observed in the egg before incubation (fig. 287, over m). It 

 is not unimportant to observe that these, the earliest observ- 

 able changes, not unfrequently take place in eggs that are laid 

 in summer, and when the weather is very warm, though, of 

 course, much short of brood-heat. 



[ 483. About the middle 

 of the first day, after from 

 twelve to fifteen hours of in- 

 cubation, the blastoderma, 

 or germinal membrane, is 

 completely detached from 

 the vitellary membrane, and 

 may be cut out as a con- 

 nected lamina, and washed 

 away from the membrane of 

 the yolk (figs. 323 and 324 . ) 

 The germinal area (area pel- 

 lucida s. germinativa) has 

 now an elongated, often a 



Fig. 323.-Vitellus or yolk after somewhat pyriform appear- 

 from twelve to fourteen hours' incuba- ance (figs. 323 and 325, 6), 

 tion, of the natural size (this and the and is two lines in length, 

 other figures of the vitellus look larger rpj ie darker vascular area 

 than proper, from their having been , fi 323 and 325 ^ hag 

 placed in flat saucers to be drawn, by \ , , , \ , , 



which they became somewhat flat- also lengthened out, and the 

 tened) : a, the yolk ; 6, area pellucida, germinal membrane extends 

 in the middle of which the notaprima- as a foliaceous formation 

 tiva, or primary streak, the first trace of indefinitely over it into the 

 the embryo is perceived ; c, outer area hal which now begin 



pellucida. the future area vasculosa. , , P 



The halones are indicated by the three to lookless regularthanthey 

 concentric circles. were originally. This outer 



