CHAPTER III 



THE DEVELOPMENT OF THE FIRST DAY 



IN speaking of the age or state of develop- 

 ment of an embryo, it is customary to 

 date from the time of the beginning of 

 the process of incubation, whether that pro- 

 cess be carried out under a hen or in an incu- 

 bator : but it must not be supposed that all 

 eggs will reach exactly the same state of de- 

 velopment at the same time. Various things 

 will influence this state ; for example, the season 

 of the year, the length of time the egg was 

 retained in the uterus before being laid, etc.; 

 so that when we speak of an egg being 

 at the thirty-six-hour stage, we shall mean 

 that the egg in question has reached a state 

 of development that is commonly reached 

 by eggs after that period of normal incuba- 

 tion. It is simply a convenient and com- 

 monly used method of speaking of embryos 

 that have reached a certain state of devel- 

 opment. 



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