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FRANKLIN PEARCE REAGAN 



generally to an age at which the normal stapes on the uninjured 

 side was well differentiated. A distinct advantage of this 

 method is that the normal side serves as a control. 



In general the results of the removal of the otocyst have 

 been made known through a previous communication (Reagan, 

 '14). 



Fig. 1 Frontal section through the otic region of a five-day chick. On the 

 left side an otocyst is present. On the right none is seen. The section is other- 

 wise almost symmetrical. All sections figured in this account are viewed from 

 their posterior faces so that the embryo's left corresponds to the reader's left. 

 P. E. C} No. 1120. Int car., internal carotid; Int. j., internal jugular; Otcst., 

 otocyst. 



A preliminary study was made of embryos at an age in which 

 the mesenchymatous tissue surrounding the normal otocyst was 

 still in a prechondral or membranous stage. Figure 1 shows a 

 section through the otic region of a chick embryo which had 

 been incubated for five days. On the unoperated side there is a 



1 Princeton Embryological Collection. 



