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CHAPTER IV. 

 THE DEVELOPMENT OF THE CHICK. 



GENERAL ACCOUNT. 

 1. Historical Sketch. 



The development of the chick has attracted great attention 

 on account of the ease with which embryos of any desired age 

 may be obtained, and of the shortness of the period within 

 which the embryonic development is completed. Almost all 

 the earlier investigations into the development of animals were 

 made 011 chick embryos, and it is round the chick that the most 

 famous embryological controversies have centred. Even at the 

 present day, 011 account of their great convenience for laboratory 

 purposes, chick embryos usually afford the material from which 

 the student derives his first lessons in practical embryology. 



Embryology as a science is barely three centuries old ; the 

 earliest descriptions and figures of the development of the chick 

 within the egg, that are of any real value, are contained in two 

 treatises published by Fabricius, professor at Padua, in 1600 and 

 1604. Half a century later, Harvey added important details in 

 his ' Theoria Generationis ; ' and towards the close of the seven- 

 teenth century, in 1687, Malpighi published the first accounts 

 of chick embryos based on microscopical examination. 



During the eighteenth century facts accumulated rapidly, 

 but the theories quite outpaced them ; and the current doctrine 

 throughout the century, supported by many, and notably by 

 Haller, was that of Preformation, according to which the chick 

 was stated to be present in the egg at the time it is laid ; all its 

 parts and organs being there from the beginning, but in an. 

 extremely minute and unexpanded condition ; the development 

 of the embryo being regarded as a process comparable to the 

 unfolding and enlargement of the several parts of a bud to form 

 the perfect flower. 



