OUTLINE FOR LABORATORY STUDY OF THE CHICK 



The objects of laboratory study of the embryos are as follows: 



1. To study the living embryo. 



2. To study the entire embryo: 



With the dissecting microscope, as an opaque object. 

 With the compound microscope after killing, hardening, clarifying, 

 and mounting. 



3. To study embryos by dissection, in later stages. 



4. To study the serial sections with the compound microscope. 



THE LIVING EMBRYO 



The egg is opened under warm physiological salt solution: 0.8 

 per cent, sodium chlorid in distilled water heated to a temperature 

 of 3 8C. 



Gradually pick away the shell at the large end. Note that there 

 are two membranes and an air cell. Strip of the membranes. 

 When sufficient shell and membranes have been removed from the 

 large end, invert the open end of the egg in the salt solution and 

 allow the contents to flow out. Care must be taken not to break the 

 yolk. The embryo, or blastoderm, lies upon the surface of the 

 yolk, which is usually turned with this body uppermost. Separate 

 the blastoderm by cutting around the outside of the area vasculosa. 

 In doing this a small pair of slightly curved scissors is needed. After 

 the embryo, or blastoderm, has been separated, gently float it into 

 a watch crystal with the flat bottom submerged in the salt solution. 

 The watch crystal with its contents may now be gently lifted out. 

 Next remove the vitelline membrane. The vitelline membrane is 

 the delicate transparent membrane covering the blastoderm. The 

 embryo is now ready for study. 



THE PREPARATION FOR STUDY OF ENTIRE EMBRYOS AND SECTIONS 



The following processes may be used in killing embryos up to 

 four days, or ninety-six hours, of age. After removing the embryo 

 as described above, spread the blastoderm out in the watch crystal 

 and pipette off the salt solution. Allow it to stand till the edge of 



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