DEVELOPMENT OF THE CHICK (2) 



1. Place an egg, which has been incubated three days, in a finger-bowl 

 of warm (about 39° C.) normal salt solution. Turn the blunt end of the 

 egg to your right and hold it, fully submerged, with one hand, and, 

 with the other, carefully insert the point of the scissors in the center of 

 the blunt end. Be very careful to use only the extreme tips of the scissors 

 in cutting the shell. While holding the egg in the same position continue 

 the cut entirely around the egg a little below the equator, and then lift 

 off the upper portion of the shell, leaving the rest of the egg, including 

 the lower portion of the shell, with the embryo, immersed in the salt 

 solution. 



2. Examine, with the dissecting microscope, the translucent embryo 

 lying on the yolk in the center of the vascular area, noting how it is 

 placed with reference to the long axis of the egg. Note the beating 

 heart, the vitelline arteries and veins which pass out to the side 

 from the middle of the embryo, and the anterior vitelline vein which 

 runs under the anterior portion of the embryo. Determine the pulse 

 rate. Make a drawing of the entire specimen, with the embryo in 

 place, to show the structures observed. 



3. Carefully make a circular cut, with small scissors, through the egg 

 membrane, just outside the limit of the vascular area. With fine for- 

 ceps take hold of an edge of the detached area and very gently separate it 

 and the attached embryo, from the underlying yolk. Hold the detached 

 portion with the forceps below the surface of the liquid, and with the 

 other hand immerse a watch glass in the liquid. Carefully float the em- 

 bryo into the watch glass, keeping it at all times below the surface of the 

 liquid. Gently raise the watch glass, with the embryo floating in it, and 

 remove entirely from the finger-bowl, taking great care not to lose the 

 embryo. With a pipet draw off a considerable portion of the fluid around 

 the embryo, and replace with a fresh supply of warm salt solution. 



4. Examine the embryo with the dissecting microscope, and identify 

 the structures which you previously noted in the permanent preparation 

 of the three-day chick embryo. Under the low power of the compound 

 microscope observe the movement of the red blood corpuscles in the 

 blood vessels. Add warm salt solution from time to time and note the 

 effect upon the pulse rate. 



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