EGGS IQ! 
observable in the eggs of some other birds, as the STorKS, Ciconiide. 
Many Water-fowls, and particularly the Ducks, Anatidz, lay eggs 
with 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, Podicipedidx, 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 Owns, Strigidx, and some of the Picariz—especially those 
which lay the glossy eggs above spoken of—are 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 most 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 Limicolz and some of the Alcidz 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 which invariably 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 by the 
brooding parent. Other eggs as those of the SAND-GROUSE, Ptero- 
cleid#, are elongated and almost cylindrical for a considerable part 
of their length, terminating at each end obtusely, while eggs of the 
GREBES, Podicipedidx, 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 GuiLLEeMmot, Alca troile, and the 
RAVEN, 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 (Jbis, 1860, p. 74), yet no other difference that can be deemed specifis 
has as yet been established between the birds of the north and of the south. 
1 A great deal of valuable information on this and other kindred subjects is 
given by Des Murs, 7'raité général d’Oologie ornithologique (8vo, Paris : 1860). 
