THYROID FEEDING AND SEX CHARACTERS. 



367 



does not appear. There are exceptions to this rule, but in these 

 cases, the rectrices are small and more or less atypical. There is 

 some variability in the form of the first rectrices in the female, the 

 stoutness and placement of the feathers and the shape of the 

 feather tips being most frequently affected, less often the number. 

 But whatever their form, the rectrices are characteristically 

 absent in the male, present in the female. 



FIG. 2. R. I. R. male (No. 12 of Table I.) twelve weeks old, thyroid fe'd for eight 



weeks. Rectrices well developed. 



In thyroid-fed males, they are characteristically present also, 

 appearing about the time they appear in normal females. Fig. 2 

 is from a photograph of No. 12, Table I., twelve weeks old. Fig. 

 3 is another thyroid-fed bird, aged twelve weeks, being No. 15, 

 Table I. In each case the head is typically male, the feathering 

 typically female. Comparison of Figs. 2 and 3 with Figs. 4 and 5 



