250 



T. H. MORGAN. 



that the results shall be clean cut it is necessary that the entire 

 testis be included in the ligature, for, if even a small piece is left, 

 it may subsequently enlarge and make the outcome less complete. 



FIG. 4. Original feathers a-e of Fig. 3, and later feathers, a 1 -*? 1 , a"-e 2 , a 3 -e 3 , 

 July 7, September 17, and March 13, 1920. 



In fact, as the following cases show, only one case of the four 

 was completely successful, although all of the other three cases 



FIG. 5. Same as Fig. 3, after ligation, March 2, 1920. 



were sufficiently successful to cause some change in the plumage 

 in the direction of cock-feathering. 



