CHAPTER VI 



THE DEVELOPMENT OF THE FOURTH DAY 



ON opening an egg at the end of the fourth 

 day of incubation (Fig. 72), one is 

 struck with the increase in size of the 

 embryo, which now, on account of the rapid 

 absorption of the white of the egg, lies so close 

 to the shell that the latter must be removed 

 with some care, in order that the embryo may 

 not be injured. 



The germinal membrane now embraces 

 about half of the yolk, and the vascular area is 

 very prominent, though the sinus terminalis 

 has already begun to diminish in distinctness. 



The distinctness of the outlines of the em- 

 byro is somewhat obscured by the amnion, 

 which now forms a complete covering over 

 it. There is, as yet, very little fluid in the 

 amniotic cavity, so that the inner amnion 

 forms a very close investment of the embryo 



(Fig. 57). 



The folding off of the embryo has continued, 



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