RICHARDSON'S SKUA. 



357 



It seems to me that these ornithologists have mistaken immature birds for 

 intermediate forms. Booth's observations appear to prove that inter- 

 mediate forms are not found at the breeding-grounds. If cross-breeding 

 be the rule, as he asserts, a few generations would amalgamate the two 

 forms ; and if the theory of Saunders and Hancock were correct, only in- 

 termediate forms should be found at the breeding-grounds. Richardson's 

 Skua appears to me to be, like the Pomarine Skua, a dimorphic species, 

 and the progeny of a light and dark bird appear, when adult, to resemble 

 one of their parents. 



