4 ARKIV FÖR ZOOLOGI. BAND 12. N:0 7. 



breeding colony, and from all its behaviour could be assumed 

 to have bred. The summer 1917 I saw another specimen 

 with dark markings on the tail sitting on eggs. — 



This hybrid in summer plumage is, as the figure (Pl. 3) 

 proves, paler grey on the mantle than in the winter plumage 

 described above, but it is nevertheless somewhat darker 

 than that of L. leucopterus. The bill has now the yellow 

 colour as in the adult birds, and the red spöt is quite deve- 

 loped. The feet are påle pinkish grey or whitish. 



The hybrid specimen which died the 20th of July 1918 

 is, of course, in fuliy adult plumage with the tail pure white. 

 The grey of the mantle is darker than in Larus leucopterus 

 and resembling that of the specimen of Larus cachinnans 

 from Kossogol mentioned above. On the other hand the 

 mantle of this hybrid Gull is paler than that of Larus fuscus 

 affinis (from Ireland), but if a Larus leucopterus, this hybrid 

 specimen, a L. fuscus affinis, and a true L. fuscus are laid 

 side by side in the order mentioned they form a most inter- 

 esting continuous series from light to dark. This is a fact 

 which appears to be of a certain importance and indicates, 

 that the colour differences between these Gulls are due only 

 to the greater or less amount of one and the same kind of 

 pigment in the feathers. The black-backed and grey-backed 

 Gulls thus represent only different degrees of pigmentatioii . 



With regard to the colour of the feet it is to be noted 

 that the yellow feet of the male parent, Larus fuscus, is not 

 inherited by the hybrid offspring, which retains the pinkish 

 feet of the mother, L. leucopterus. The yellow colour of the 

 feet is thus in this case a recessive character. 



On the other hand black pigment to a greater or less 

 extension on the primaries has been inherited by the hybrids 

 from their father, L. fuscus. This positive paternal character, 

 presence of black pigment on the primaries, is thus dominant 

 against the negative maternal character, absence of pigment 

 on the said quills. This was rather to be expected, if it is 

 taken into consideration that black on the primaries is of a 

 very common occurrence among the Gulls, and that the dark 

 bands on the tips of the primaries in the immat ure Larus 

 leucopterus appears to indicate a former pigmentation of 

 those parts, even among the ancestors of this species. 



The extension and distribution of the black on the pri- 



