U22 



EXPERIMENTAL CHICK EMBRYOLOGY 



THE REMOVAL OF CHICK BLASTODERMS OR EMBRYOS 



Early Blastodenna : 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 2/5 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 blas- 

 toderm ^" 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 be- 

 ing 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. 



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 • 

 vitelline 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 dissecting needles, 

 beneath a dissecting microscope. 



The young blastoderm is extremely yolk-adherent. Some investigators inject warm 

 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 auck the blastoderm (after re- 



■ — SOMITE 

 O —ENTODERM 

 SR-SINUS 



RM0M80IDALIS' 

 # —NEURAL CREST 

 LP-LATERAL PLATE 

 M —HEAD MESODERM 



^-MEART 



®- CMOftDA 



O-NEPHfiOS 



• - ERYTHROCYTES 



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 the boundar 

 assumptions 

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 accurate ex 



Tills c 

 based large 

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In tlie definitive primitive streak blastoderm of the clilck. The 

 own at the left while the invaglnated material is seen In the 

 upted line on the left side of the anterior streak region marks 

 e ectoderm and the still unlnvaglnated mesoderm. This Is on the 

 nation Is as yet Incomplete and that future Invagination will be 

 tlned to form the embryo proper. All mesodermal boundaries need 

 erlflcatlon. 



Is drawn by Rudnlck (l'J44 Quart. Kev. md. 19:187) and Is 

 f Pasteels. In addition, there have been contributions from the 

 cells), Wolff (morpliogenesls of trunk and tall), and Ynteraa 



