242 PRACTICAL DIRECTIONS. [APP. 



1. Lying across the long axis of the egg, the pellucid 

 area, in the middle of which the embryo may be 

 obscurely seen as a white streak. 



2. The mottled vascular area, with the blood-vessels 

 just beginning to be formed. 



3. The opaque area spreading over the yolk with the 

 changes in the yolk around its periphery. 



4. (With a simple lens), the contractions of the heart; 

 perhaps the outlines of the head of the embryo may 

 be detected. 



C. Removal of the embryo. 



Plunge one blade of a sharp fine pair of scissors 

 through the blastoderm, just outside the outer margin 

 of the vascular area, and rapidly carry the incision 

 completely round. Until the circle is complete, avoid 

 as much as possible any agitation of the liquid in the 

 basin. 



With a little trouble, the excised blastoderm may 

 now be floated into a watch-glass, care being taken to 

 keep it as flat as possible. With a pair of forceps or 

 with a needle, aided by gentle shaking, remove the 

 piece of vitelline membrane covering the blastoderm. 



If any yolk adheres to the blastoderm, it may with 

 a little gentle agitation easily be washed off. Some- 

 times it is of advantage to suck up the yolk with a 

 glass syringe, replacing the fluid removed with clean 

 (*75 p. c.) salt solution. 



The blastoderm should now be removed from the 

 watch-glass to a microscopic glass slide ; since it is 

 difficult in the former to prevent the edges of the 

 blastoderm from curling up. 



The transference may easity be effected, if both the 

 watch-glass and slide are plunged into a basin of clean 

 warm salt solution. With a little care, the blasto- 

 derm can then be floated from the one to the other, and 

 the glass slide, having the blastoderm with its upper 

 surface uppermost spread flat upon it, very gently 

 raised out of the liquid. 



