On the Hybridising of Duels. 259 



myself with the hare mention of a few common species to 

 exemplify the different classes of these spots. 



The Kingfisher (Alcedo ispida), shows the various head 

 poecilomeres very clearly, and as examples of inconspicuous 

 differences on these tracts, the rump of the hen Sparrow 

 (Passer domesticus) and hen Chaffinch (Fringilla coelebs), the 

 malar stripe and dark ear patch of the hen Yellow Bunting 

 (Emberiza citrinella), and the dark ante-orbital patch of the 

 Barn Owl (Striae flammea) , are familiar examples. 



And, lastly, as an instance of the class where a few white 

 feathers frequently, but not invariably, appear, the young of 

 the Cuckoo (Guculus canorus) forms a good example. 



These spots may, however, sometimes appear in a transitory 

 manner, as, for instance, when a change of plumage (not 

 necessarily moult) is occurring, and in the paper referred to 

 above the instance is brought forward of a young male 

 Shoveler (Spatula dypeata) in which the metallic colour on 

 the head first showed itself on the post-orbital and auricular 

 poecilomeres, gradually meeting and joining up across the 

 head with the crown and occipital poecilomeres, and 

 then finally spreading forwards, and it may be well to 

 note that the joining up of the auricular and post-orbital 

 poecilomeres formed a metallic patch similar in size and posi- 

 tion to that found in the <$ Teal (Querquedula crecca), and, 

 further, in the last stage, when the whole head, except the 

 portion round the beak, was metallic, the markings were 

 similar to those found permanently in the hen Scaup 

 (Fuligula mania). Now these resemblances taking place in 

 the normal pure-bred wild Shoveler, the question of 

 reversion does not come in, and no one would suppose 

 these resemblances due to anything more than transitional 

 variation, and it is the object of this portion of the paper to 

 show that variation in colour follows along definite lines. 



As a further illustration of how widely spread these lines 

 are throughout the Mammalian and Avian kingdoms we 

 may note the assumption of the brown head in the case of 

 the Black-headed Gull (Larus ridibundus) which invariably 

 follows every year on lines similar to those related in the 

 case of the Shoveler, and, as I have before pointed out, the 



