E. LÖNNBERG, HYBRID GULLS. 19 



been made probable that in two points the hybrids represent 

 an ancestral stage, it appears quite possible that the same 

 is the case with regard to the third as well, viz. the colour 

 of the mantle, or that tbis grey colour is more primitive 

 than both the »påle pearl-grey» of L. glaucus, and the slaty 

 blackish of L. marinus. 



These two species represent therefore the opposite ex- 

 tremes of the same series. L. glaucus is the arctic form 

 which living among ice and snow has löst its pigment as an 

 adaptation to the environment. L. marinus again has be- 

 come more strongly pigmented as it lives on the always 

 open, dark sea and breeds and rests on dark rocks. Both 

 are too strong to directly need this adaptation for protective 

 purpose, but the fact remains that many animals, even those 

 which do not need protective resemblance, nor try to conceal 

 themselves nevertheless often with regard to their colours 

 agree with their surroundings. That these two species really 

 belong to the same series of forms and are rather closely 

 related is proved by the fact that they so readily interbreed 

 with each other, and that the hybrid offspring is fertile. 

 Larus marinus and L. glaucus stånd in the same relation to 

 each other as L. fuscus and L. leucopterus. 



From this may also the conclusion readily be drawn 

 that the usual grouping of these Gulls in systematic works 

 acording to the black (resp. dark-slate coloured), or grey 

 mantle is wholly artificial. The same is also the case with 

 the division in such Gulls that have »quills mostly black», 

 and such that have the »quills devoid of black; mostly påle 

 grey or white». Quite the opposite is the case. We have 

 found, that two of the darkest species are so closely related 

 respectively each with one of the two palest species, that 

 they spontaneously interbreed and produce an offspring, 

 which, in spite of the parents belonging to different »syste- 

 matic groups» has proved to be fertile,^ a rather rare fact. 

 By this appears to open a new way to a better understanding 

 of the real affinities among the Gulls with less consideration 

 of the colour, or rather the intensity of the same. 



Since the above was written I have had the pleasant 

 opportunity of examining a couple of young hybrids which 

 constitute a second hybrid generation, as their parents were 



^ At least sometimes. 



