EMBRYOLOG Y. 1 51 



Work thence forward through the head-fold 

 and make out all its relations. 



Observe : the vitelline veins, the ducts of 

 Cuvier, the heart (follow out its turns), the 

 pericardia! cavity, the aortic arches. 



Now begin at the front end of the series and, 

 remembering the cranial flexure, make out 

 the various parts of the brain, the develop- 

 ment of the eye, the internal ear, the olfac- 

 tory pits, the gill-slits (in the neck region), 

 the - archenteron and its derivatives : the 

 lungs, the liver, and the pancreas (?). 



Study also the origin of the cranial nerves 



and the Wolffian ducts and their tubules. 

 Sketches to show these structures. 

 3. The living embryo. 

 With the points of strong scissors pierce the broad 



end of the shell to allow the air to escape. 



Place the egg in warm normal salt solution 



(38 degrees (7.,) cut away or break away with 



forceps the upper part of the shell, and examine 



in situ. 



Observe ivith a hand-lens : 



(a) The blastoderm and its areas. 



(6) The position and form of the embryo. 



(c) The heart, etc. 

 With fine sharp scissors cut through the blastoderm 



entirely around the outside of the area vascu- 



losa, float it off into a thin watch-glass, care- 



