CHAPTER IV 

 THE DEVELOPMENT OF THE SECOND DAY 



IT will be convenient, and will facilitate the 

 study of sections, in the laboratory, to 

 divide the second day into two parts ; 

 describing first the changes that take place 

 from the twenty-fourth to the thirty-sixth hour, 

 and then those that take place during the 

 second half of the day. 



FROM THE 24TH TO THE 36TH HOUR 



During this period the embryo not only 

 becomes much more clearly outlined, but its 

 texture becomes more firm, so that, while it 

 was very difficult to remove an eighteen-hour 

 embryo from the egg without tearing, it is 

 quite an easy matter to remove an embryo 

 of thirty to thirty-six hours. 



The medullary folds are rapidly coming 

 together, and, by the thirty-sixth hour, the 

 entire anterior region is closed in to form the 



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