Hematoxylin-stained, 33-hour Chick 185 



that can be employed, the more easily will the embryo be removed. The 

 easiest method is to take blunt forceps in the left hand and with it grip 

 the extraembryonic areas of the chick well outside the sinus terminalis. A 

 certain amount of drag is placed on it so that the vitelline membrane is 

 wrinkled, and then with a large pair of scissors a transverse cut is made 

 directly away from the operator about y 3 in. outside the sinus terminalis 

 on the side of the embryo opposite that which is held by the forceps. This 

 initial cut should be at least % in. long and should be made firmly. Two 

 cuts, at right angles to the first, should be run on each side of the embryo. 

 The part gripped with the forceps should be released, and the free 

 edge, where the first cut was made, gripped so that the embryo can be 

 folded back away from the yolk. It is now relatively easy to sever all con- 

 nection between the embryo and the underlying materials by a fourth 

 cut. The embryo, held by the forceps in the left hand, will now be float- 

 ing free in the saline solution. The embryo is much stronger than it looks 

 and will not be damaged, provided the tips of the forceps are kept under 

 the saline solution. 



The embryo must be transferred to clean saline solution, preferably in 

 another finger bowl. This transfer may be made either with a very wide- 

 mouthed pipette of the eye-dropper type or by scooping it up in a 

 smaller watch glass with plenty of saline solution and transferring it to 

 the fresh solution. Here it should be picked up again by one corner with 

 the forceps and waved gently backward and forward to remove the ad- 

 herent vitelline membrane as well as such yolk as remains. At this stage 

 the embryo should be examined to make sure that the heart is beating 

 and that it is in fit condition for fixation. 



The embryo is now scooped out on one of the Syracuse watch glasses 

 with as little water as possible. Next it is necessary to persuade it to 

 flatten on the bottom in an upside-down position, that is, so that the 

 portion of the embryo that was previously in contact with the yolk is now 

 directed toward the operator. To determine which side of the embryo is 

 uppermost requires considerable practice unless the primary curvature 

 of the head toward the right has already started. The best point of exami- 

 nation is the heart, which lies, of course, on the lower surface of the 

 embryo. Having maneuvered the embryo in the saline solution in the 

 watch glass until it is in the upside-down position required, the water 

 should be drained off with the aid of a pipette, which is run rapidly with 

 a circular motion around the outside of the blastoderm while the water 

 is drawn up. As experience will soon show, any attempt to drain the 

 water up a stationary pipette will result in the embryo being drawn out 

 in the direction in which the water is being sucked. A little practice in 

 running the pipette around and around the outside of the blastoderm 

 and about a millimeter away from it will enable the operator to strand 



