CHAPTER IV. 



THE CHANGES WHICH TAKE PLACE DURING THE FIRST 

 HALF OF THE SECOND DAY. 



General development. In attempting to remove 

 the blastoderm from an egg -which has undergone 

 from 30 to 36 hours' incubation, the observer can- 

 not fail to notice a marked change in the consist- 

 ency;^ of the blastodermic structures. The excessive 

 delicacy and softness of texture which rendered the 

 extraction of an 18 or 20 hours' blastoderm so difficult, 

 has given place to a considerable amount of firmness; 

 the outlines of the embryo and its appendages are much 

 bolder and more distinct; and the whole blastoderm 

 can be removed from the egg with much greater ease. 



In the embryo itself viewed from above one of the 

 features which first attracts attention is the progress 

 in the head-fold (Fig. 27). The upper limb or head 

 has become much more prominent, while the lower 

 groove is not only proportionately deeper, but is also 

 being carried back beneath the body of the embryo. 



The medullary folds are closing rapidly. In the 

 region of the head they have quite coalesced, a slight 

 notch in the middle line at the extreme front marking 



