334 Procecdinfjs of the Royal Physical Society. 



The Black-heaclecl Gull is a species which has a great 

 variety of colour in its eggs, as the specimens now exhibited 

 show — so much so, indeed, that an ordinary observer 

 would scarcely believe it possible that all these eggs, 

 varying at once in size and colour, belonged to the same 

 species of bird. I am indebted to the Eev. J. M. Joass, 

 minister of Golspie, Sutherland, for being able to exhibit this 

 very curious collection of eggs. From the bird nesting in 

 great numbers together, often in some island in an inland 

 loch, it is, of course, comparatively easy for the collector to 

 go among the number of nests and make selections of the 

 varieties of those eggs season after season. In a note to the 

 writer, Dr Joass states that the eggs were obtained from an 

 island in Loch Salachaidh, parish of Golspie, Sutherland, 

 5 miles inland, and about 550 feet above sea-level. " The 

 only birds observed on the island," he states, " were the 

 Black-headed Gull and Common Gull in about equal num- 

 bers. Some wild geese and teal were seen on the loch. 

 A widgeon's nest with eggs hard set was found in long 

 heather near the loch on May 15th, 1882." 



The general colour of the eggs of this bird is an olivaceous 

 green, differing in intensity, with brownish and purplish 

 spots. The four eggs now shown illustrate the more ordinary 

 colours, but these, it will be seen, show a very great range 

 from a dark olive colour, covered with brown and purplish 

 sjoots, to a very light greenish colour, with spots and blotches 

 of dark brown intermixed with lighter purplish blotches, one 

 egg being almost white, with a few very faint spots of purple 

 scattered over it. These eggs have the spots and blotches 

 scattered pretty generally over their surfaces ; there is one, 

 however, which shows a somewhat similar but duller greenish 

 body colour, but which has the greater number of the spots 

 collected into a sort of blurred ring round the larger extremity 

 of the eq-o-. 



The four eggs now exhibited show no greenish coloin- at 

 all, but a general reddish tone, one being covered with bright 

 reddish brown and fainter purplish spots ; the others showing 

 a general less strongly defined spotted character, the spots 

 diniiniahing both in aize and intensity of colour. Two of the 



