E. LÖNNBERG, HYBRID GULLS. 9 



On the other hand it cannot be doubted that Larus 

 leucopterus is a product of a development in an opposite 

 direction by loss of pigment. That its ancestors really have 

 had partly black-pigmented outer primaries cannot only be 

 concluded per analogiam, but it is also suggested by the 

 presence of dark or dusky bands on the primaries of the im- 

 matnre birds, as bas been mentioned above. The general 

 reduction of pigment in Lams leucopterus manifes ting itself 

 in its very påle mantle, and its complete loss of the black 

 pigment on the primaries may be regarded as an adaptation 

 to the surroundings of ice and snow in its arctic home 

 country.^ — Larus glaucns may of course be assumed to be 

 the product of a similar adaptive development. — 



The parents of the hybrids described above represent 

 thus according to my opinion the extreme stages of a deve- 

 lopment in quite opposite directions, and the product of their 

 crossing displays an intermediate, more primitive, or generalised 

 type. It is with other words a reversion to an ancestral form. 



With regard to the size of these hybrids it may be men- 

 tioned that the length of the wing of the specimen received 

 by the museum 20/7 1918 is about 438 mm. In the still living 

 specimen the length of the wing is about 455 mm. The 

 younger hybrid has a much shorter wing, but as it is much 

 worn at the tip an exact measurement cannot be given. 

 Probably it has not attained a length of 400 mm. The length 

 of the tarsus of the adult hybrid is about 70 mm. The bill 

 is strongly built with a length of the culmen amounting to 

 about 56 mm. In the still living specimen it is about 63 mm. 

 The latter has thus remarkably great dimensions when com- 

 pared with the parents. 



2. Larus niariinis c? X larus glaucus $. 



Hybrids between different species of Gulls (Larus) seem 

 to be very rare. There appears to be hardly any records in 

 the literature about such with the exception of a statement 



^ I do not mean to say by this that this adaptation has been deve- 

 loped as a protective resemblance to the surroundings, which is not 

 needed. 



