MUSEUM OF COMPARATIVE ZOOLOGY. 



207 



varies from fourteen to twenty. Specimens with sixteen are tolerably 

 frequent. Yet one of the principal characters urged as separating the 

 B. Hutchinsii from the B. canadensis is the possession of two more 

 feathers in the tail by the latter tlian the so-called B. Hutchinsii is 

 assumed to have. In Bernicla brenta the usual number is sixteen, 

 but in different specimens they vary from fourteen to eighteen. A 

 greater, or less amount of variation in the number of the feathers of 

 the tail is more or less common to numerous other species of the duck 

 tribe. An odd number is even quite frequent, one half of the tail hav- 

 ing normally one more feather than the other. 



Variation in the Relative Length of the Tarsus and Toes. — A com- 

 mon feature in modern generic and specific diagnoses is a statement of 

 the ratio the length of the tarsus bears to the length of the middle toe 

 or to the hallux, and the relative length of the hallux to the outer or 

 inner toe, as though we had here constant structural proportions. The 

 following table (Table G) shows that such is not the case, the varia- 



Table G. — Relative Length of Tarsi and Toes. 



