51. THE REMOVAL OF CHICK 

 BLASTODERMS OR EMBRYOS 



Early Blastoderms: The chick blastoderm always floats around to the upper surface of 

 the heavier yolk mass. Hold the egg in the palm of the hand for a minute or two and then 

 crack the underside of the shell on the edge of a finger bowl 2/3 full of Locke's or saline 

 solution, and (in the manner of cracking an egg for frying) allow the egg contents to flow 

 out into the solution. The blastoderm will shortly move around to the most dorsal posi- 

 tion. 



Grasp the chalaza or the yolk on one side with forceps held in the left hand (for right 

 handed operators), then, with sharp-pointed scissors, quickly cut around the blastoderm 

 1/4" from its border. This movement of the scissors can be aided by a contrary move- 

 ment of the forceps, turning the entire egg mass with the forceps as the blastoderm is 

 being cut with the scissors. The cut is made through the very thin and transparent vitel- 

 line membrane, through the blastoderm proper, and into the underlying yolk. 



AREA PELLUCIOA 

 I ^MSRYO 

 AREA VASCULOSA 



AREA VITELLINA 

 INTERNA 



AREA VITELLIN, 

 EXTERNA 

 AREA 

 VASCULOSa 



AVI 

 A VE 

 YOLK 



THE 24 HOUR CHICK EMBRYO 



THE 50 HOUR CHICK EMBRYO 

 (ALBUMEN REMOVED) 



Grasp the cut edge (vitelline membrane, blastoderm, and yolk) and roll it back from the 

 bulk of the yolk mass. Draw it away from the yolk mass. Holding the edge of the vitel- 

 line membrane with forceps work a dissecting needle around its border, and use the 

 needle to roll the blastoderm away from the membrane. Then, with a wide -mouthed 

 pipette, remove the blastoderm to a Petri dish containing 20 cc. of Locke's or Saline 

 solution. All of the yolky opaque area may now be trimmed off with scalpel or dissect- 

 ing needles, beneath a dissecting microscope. 



The young blastoderni is extremely yolk-adherent. Some investigators inject warnra 

 Locke's solution beneath the blastoderm before excising it. This raises the blastoderm 

 off of the yolk by providing an elevating vesicle of fluid beneath, separating it from the 

 yolk. Other investigators find it simpler to gently suck the blastoderm (after removal of 

 the vitelline membrane) in and out of a wide-mouthed pipette, thereby removing inost of 

 the adherent yolk. Still others play a gentle stream of medium on the surface of the in- 

 verted blastoderm, blowing the yolk granules away. 



The early stages are particularly fragile and the less handling the better. In most in- 

 stances the peripheral yolk may be trimmed away with scalpel, scissors, or even with 

 needles, and the yolk adherent to the underside of the area pellucida is negligible. It is 

 particularly difficult to handle the blastoderms of less than 18 hours without damage. 



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