Volume /.] January, n)OO. \_No. 2. 



BIOLOGICAL BULLETIN. 



THE EARLY STAGES IN THE DEVELOPMENT 

 OE THE HYPOPHYSIS OF AMI A CALVA. 



J. M. PRATHER. 1 



THE results of my work on Amia do not agree with the 

 common assumption that the pituitary body is always of epi- 

 blastic origin. This disagreement has led me to an examina- 

 tion of the literature on the subject to see if there is sufficient 

 unity of opinion among recent investigators to warrant such a 

 general conclusion. As a result it is found that a diversity of 

 opinion still prevails, and that it is unsafe to predict its origin 

 in any class of vertebrates. 



A brief classification of the various views and their respec- 

 tive advocates is of interest in this connection : K. E. von Baer 

 ('28), Huschke ('54), and F. Schmidt ('62) believed the hypophy- 

 sis to be a modified part of the brain. Reichert ('40) and His 

 ('68) claimed that it is derived from the end of the chorda. 

 Reichert ('61) and Rathke ('61) believed it to be derived from 

 the pia mater, each having changed his earlier view. Dursy 

 ('68) maintained that it is of threefold origin - - from the fore- 

 gut, the chorda, and the brain. 



The above represent the earlier but now generally discarded 

 hypotheses. The more modern views, some of which were also 

 held by the older anatomists, may be grouped as follows : 



i. T licit tJic hypophysis is of hypoblastic origin, as held by 



1 This study was undertaken at the suggestion of Dr. A. C. Eycleshymer and 

 completed under his direction in the Department of Anatomy and Histology in 

 the University of Chicago during the summer of 1899. 



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