154 PROBLEMS OF GENETICS 



distribution of the red and yellow quills of the tail especially, 

 recalls that of the black markings in the pied Canaries. As is well 

 known to students of variations some pigment-factors in some 

 animals are apparently uncontrolled by symmetry, while in other 

 specific cases symmetry is the rule. On the other hand the 

 blackness or redness of the malar patches is, I think, as a rule 

 nearly symmetrical. It should be mentioned that two of Dr. 

 Bishop's young birds belonged to the same nest, one a female 

 with red quills, the other a male with yellow. Both are without 

 crescent. 



As to the question whether certain combinations of characters 

 occur with special frequency, the evidence is insufficient to give a 

 definite answer. Among all the birds I have seen in America 

 or in England I have not yet found one having the malar patches 

 black without any nuchal crescent. Of Dr. Bishop's 8 adults 

 not one, however, showed the combination of the three chief 

 features normal for auratus or for cafer. 



Besides the two forms that we have hitherto considered, 

 several other local types exist, and these throw some further 

 light on the problem. Of these the most important in this 

 connexion is chrysoides, which inhabits the whole of southern 

 California and the mainland opposite. This remarkable form 

 is as Allen says, very different from auratus except that it has 

 the quills yellow like auratus, not red like cafer. So that we 

 find here in the extreme west of the whole distribution a type 

 agreeing in one of its chief features with the eastern type. Be- 

 tween this and cafer intergrades have, according to Allen, not 

 been found. The relations of this chrysoides are, Allen thinks, 

 rather with mexicanoides , a southern, smaller race with colours 

 more intense, which inhabits Guatemala, but however that may 

 be, it must be regarded as a cafer which has lost its red quills. 

 The island of Guadeloupe off Lower California has an island 

 form. Beyond the other side of the continent there is also an 

 island form of auratus, inhabiting Cuba, so that clearly the yellow 

 quills can extend into the tropics. 



The above account is in many respects incomplete, but it 

 suffices to give an outline of the chief facts. The whole problem 



