Grade. 

 Date.. 



EXERCISE 21 

 THE DEVELOPMENT OF A CHICK EMBRYO 



Object. To dissect and study in detail the development of the chick 

 embryo and to become familiar with the various stages in its development 

 and the relation of same to the period of incubation. 



Equipment. A number of eggs containing.embryos of the following ages: 

 36 hours, 72 hours, 7 days, 14 days, and 19 days old; petri dishes, dissecting 

 dishes, needles, and knives; drawing pencil, and a hand lens. 



Procedure. Proceed to study each of the five stages in the development 

 of the embryo in their proper order hi the following manner: 



Step 1. Break the shell very carefully and empty the contents of the 

 egg to be studied into a larger petri dish without rupturing yolk or membrane. 

 If the egg is opened under water there is less danger of rupturing the contents. 

 Step 2. Look for the following organs and structures as they may ap- 

 pear hi each successive stage: 



Area palucida Pro-vertebrata 



Inner and outer amnion Wings 



Lobes of the head Legs 



Brain Beak 



Spinal cord Eyes 



Heart Feathers 



Arteries and veins 



Step 3. Make a drawing of each stage of embryo development studied, 

 name and locate the organs and structures found. In the following table, 

 list under each age the organs seen at that period. List new organs appear- 

 ing at any period hi red. 



Step 4. Open an egg containing a 72-hour-old embryo, emptying it into 

 warm water. Observe the heart-beats. Count the rapidity of same and the 

 length of time they continue. 



Step 5. Repeat the previous step, emptying the embryo into cold water, 

 and observe the results. 



Step 6. Examine a number of embryos on the nineteenth day. Note 

 their position hi the shell and take full notes on their position. 



Leading Questions. 1. How and where is the yolk sack attached to the 

 embryo? 

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