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 with 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 fo place the eggs as soon as laid 

 immediately under the hen. Only by this means can an approximate correla- 

 tion between the stage of development and the duration of incubation be secured. 



Artificial incubators are now made to work satisfactorily.* The tem- 

 perature 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 mois- 

 ture. 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 varying ages, the exact time of laying not being 

 recorded. 



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

 eggs, ft is called the Plymouth Incubator, and is sold by Charles I. Nesmith, Reading, 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. 



269 



