LARIDAE AND STERNIDAE. 



coloration of the eggshell, as otherwise in 5. fliiviatilis the liglit 

 blue colour of the shell, even if not without exceptions, would most 

 decidedly have to be the rule, which is far from being the case. 



To me it would seem more probable that the oge of the female 

 birds forms the dominating factor in the pigmentation of the eggshell, 

 to which circumstance Morris, amongst others, drew attention in 

 respect of Buteo buteo (see the observations regarding this species 

 in my general review of the XVII. Family: Falconidae). 



Nevertheless, to Dr. Venema is due the merit of having drawn 

 attention to this point; and the subject is worth investigating. Cer- 

 tainty will however only be obtainable by means of experiments 

 with birds propagating in confinement. 



As is the case with the other Larldac, the eggs of one clutch 

 often differ mutually to a considerable extent in argentatus also. 

 Thus Dr. E. D. van Oort states that in June 1909 he found in 

 the dunes near Wassenaar a set consisting of two normally coloured 

 eggs and one egg with a heron-blue ground colour, finely speckled 

 with pale grey, and marked, particularly at the big end, with a few 

 large dark olive brown and black spots, as also with a few faint 

 greyish violet clouds. The three eggs are all of normal size. 



STERNA CANTIACA GMELIN. 



At the conclusion of my monograph -') about the cantiaca-eggs I 

 recapitulate that among the so diversified markings three types 

 are found in the main, viz: 



') Report on birds from the Netherlands received from 1 September 1908 

 till 1 September 1909, in: Notes from (he Lcydcn Museum, Vol. XXXI (Note 

 XIV, p. 218). 



^ About the markings, and the nature of their variations, of the eggs of 

 Sterna cantiaca Gmelin, in „Verslagen en Mededeelingen der Nederlandsche 

 Ornithologische Vereeniging", No. 1, p. 49—52. 



