EGGS 191 



observable in the eggs of some other birds, as the Storks, Ciconiidx. 

 Many Water-fowls, and particularly the DuCKS, Anaticlss, lay eggs 

 -w-ith a greasy or oleaginous exterior, as the collector who wishes to 

 inscribe his specimens with marks of their identity often finds to 

 his inconvenience ; but there are other eggs, as those of the Anis, 

 Crotophaga, the Grebes, PodicipecUdx, and all of the Steganopodes, 

 except Phaethon, which are more or less covered with a cretaceous 

 film, often of considerable thickness and varied by calcareous pro- 

 tuberances. 



In form eggs vary very much, and this is sometimes observable 

 in examples not only of the same species but even from the same 

 mother, yet a certain amount of resemblance is usually to be traced 

 according to the natural group to which the parents belong. Those 

 of the Owls, Strigidse, and some of the Ficarm — especially those 

 which lay the glossy eggs above spoken of — ai-e often apparently 

 spherical, though it is probable that if tested mathematically none 

 would be found truly so — indeed it may be asserted that few eggs 

 are strictly symmetrical, however nearly they may seem so, one 

 side bulging out, though very slightly, more than the other. The 

 really oval form, with which we are miost familiar, needs no remark, 

 but this is capable of infinite variety caused by the relative posi- 

 tion and proportion of the major and minor axis. In nearly all 

 the Limkolx and some of the Alcidx the egg attenuates very rapidly 

 towards the smaller end, sometimes in a slightly convex curve, 

 sometimes without perceptible curvature, and occasionally in a 

 sensibly concave curve. The eggs having this pyriform shape are 

 mostly those of birds Avhich invaidably lay four in a nest, and therein 

 they lie with their points almost meeting in the centre and thus 

 occupying as little space as possible and more easily covered hj the 

 brooding parent. Other eggs as those of the Sand-Grouse, Ptero- 

 deklx, are elongated and almost cylindrical for a considerable part 

 of their length, terminating at each end obtusely, while eggs of the 

 Grebes, Podicipedidse, which also have both ends nearly alike but 

 pointed, are so wide in the middle as to present a biconical appear- 

 ance.^ 



The size of eggs is generally but not at all constantly in pro- 

 portion to that of the parent. The GUILLEMOT, Alca trode, and the 

 Eaven, Corvus corax, are themselves of about equal size ; their eggs 

 vary as ten to one. The Snipe, Scolopax gallinago, and the Black- 

 bird, Turdus merula, differ but slightly in weight, their eggs remark- 

 ably. The eggs of the Guillemot are as big as those of an Eagle ; 



surface, without any punctures, whereas southern specimens are rough as though 

 pock-marked {Ibis, 1860, p. 74), yet no other difference that can be deemed specifio 

 has as yet been estalilished between the birds of the north and of the south. 



^ A great deal of valuable information on this and other kindred subjects ia 

 given by Des Murs, TraiU giniral d'Oologie ornithologiquc (8vo, Paris : 1860). 



