CHAPTER IX 



THE DEVELOPMENT OF THE MAMMAL 



SINCE the development of man and other 

 mammals is, in most particulars, strik- 

 ingly like that of the chick, as described 

 in the preceding chapters ; and since there are 

 already available several excellent text-books 

 that discuss the embryology of mammals, the 

 purpose of this chapter will be to point out 

 the main differences between the embryological 

 processes of the chick and those of man or 

 other higher mammalia. These differences are 

 due, largely, to the differences in the amount 

 of food yolk in the ovum, which causes the 

 hen's egg to be many thousand times larger 

 than that of the ordinary mammal. 



As has been seen in the preceding chapters, 

 the great mass of yolk in the ovum of birds 

 serves as food for the developing embryo, 

 so that, at the time of hatching, the young 

 chick has acquired, without outside aid, essen- 

 tially the adult form. In the ovum of man, 



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