XXXVII. 



THE DEVELOPMENT OF THE FOURTH DAY 



On opening an egg which has been incubated for four days, the 

 great increase in size of the embryo is the most noticeable feature. The 

 germinal membrane now covers almost one-half of the yolk, and the 



L 



Fig. 301. 



1, Median sagittal section of 82 hour chick embryo. 2. Whole mount to show 



regions from which A to O are cut. Sections A=A A; B B B; etc. (Re- 

 drawn from Duval.) 



