CHAPTER V. 

 STUDY OF YOUNG CHICK EMBRYOS. 



Method of Obtaining Embryos. 



Fertile eggs can usually be obtained from dealers, who can supply them in 

 quantities as needed, or hens may be kept wifh little trouble especially for the 

 purpose. In that case the hen herself will be found the best incubator, for the 

 number of eggs which develop normally under a hen is larger than in an artificial 

 incubator, and abnormalities of development are less frequent. A good setter will 

 remain upon the eggs, even though some are removed and replaced by fresh ones, 

 for about a month. She should be plentifully supplied with water and soft food, 

 which is best kept at a little distance off, so that she will be obliged to leave the 

 eggs to feed. A box that is somewhat secluded, and affords some protection, 

 warmth, and shelter from the light, should be provided. In order to obtain the 

 most accurate results it is desirable to place the eggs as soon as laid immediately 

 under the hen. Only by this means can an approximate correlation between the 

 stage of development and the duration of incubation be secured. 



Artificial incubators are now made to work satisfactorily.* The temperature 

 of an incubator should be maintained at about 38 C. (100.4 F.). It should on 

 no account be allowed to rise above 40 C. (104 F.), for that destroys a portion 

 of the eggs and causes the production of many abnormalities in the remainder; and, 

 if possible, a fall to a lower temperature should be avoided, although the results of 

 a lower temperature are less disastrous. No incubator should be used which does 

 not permit a constant supply of fresh air and of moisture. The date should always 

 be marked on each egg when it is placed in the incubator. If a number of eggs 

 from a dealer are artificially incubated the same length of time, they are pretty sure 

 to cover a considerable range of stages, as, of course, 'eggs so supplied are of vary- 

 ing ages, the exact time of laying not being recorded. 



In this work two stages of the chick are especially studied. The first stage 

 studied is that of a chick with seven segments, which is normal after about twenty- 

 seven hours' incubation. The second is normally produced after about forty-six 

 hours' incubation. The embryo should have about twenty-eight segments and three 



* The one used at the Harvard Medical School is heated by a kerosene lamp and has a capacity of 100 

 eggs. It is called the New Method Incubator, and was purchased from M. A. Coffin, Burlington, Mass. In the 

 market other incubators may be found, doubtless equally good, among them patterns adapted for the use of gas 

 where that is preferred. 



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