368 OSCAR RIDDLE. 



Explanation of Plate XIV. 



Fig. 22. Four rectrices of chick "dosed" with amyl nitrite on two succeeding 

 nights. (Several feathers had their tips cut off at approximately 18 mm. from the 

 skin, so as to be able later to identify the region affected by the low blood pressure 

 produced. ) Points marked b are the fault-bars produced on the nights of the experi- 

 ment. 



Fig. 23. A fifth rectrix which in addition to the usual fault-bars shows a longi- 

 tudinal fault-bar for lb beginning with the second night of the experiment. 



Fig. 24. A rectrix from the control chick. These feathers show no defects. 



