COMPARATIVE OOLOGY OF NORTH AMERICAN BIRDS. 463 



and more resembles that of apteryx."* In form they are more or less 

 globular and completely opaque. This last-named character in the 

 eggs of birds is a very interesting one to the student. Prof. Newton, 

 who has thrown so much light for us upon the subject of avian oology, 

 remarks upon this point that " 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 par- 

 ents belong. Those of the Owls (Strigidw and of some of the Picariw — 

 especially those which lay the glossy eggs above spoken of — are often 

 apparently spherical, though it is probable that if tested mathematic- 

 ally none would be found truly so; indeed it maybe 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 position and 

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

 and some of the Alcidce 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 4 in a nest, and therein they lie with their points almost 

 meeting in the center and thus occupying as little space as possible 

 and more easily covered by the brooding parent. Other eggs, as those 

 of the Sand Grouse ( Pt&roeleidce), are elongated and almost cylindrical 

 for a considerable part of their length, terminating at each end obtusely, 

 while eggs of the Grebes (PodicipedidcB), which also have both ends 

 nearly alike, but pointed, are so wide in the middle as to present a 

 biconical appearance.! 



The remarkable variation in both color and form of the eggs of many 

 of our North American birds can nowhere be better studied and appre- 

 ciated than is the splendid quarto (with its many beautifully colored 

 plates), recently published by Oapt. Bendire,| and in the treatises of 

 corresponding magnitude of other authors, as those of Wolley, Thiene- 



*Journ. fur wissensch. Zoologie., 1871, pp. 330-355. Mr. Lucas, of the U. S. 

 National Museum, tells me that the egg of Apteryx is white, and the shell like that 

 of a hen's egg. 



tNewton, A.: Art. "Birds" Encycl. Brit., ninth ed., vol. m, p. 775. See also in 

 this connection the valuable contributions to the subject by dea Murs, Triate" gdneral 

 d'Oologie ornitbologique (8 vo. Paris: 1860). 



t Beudire, Charles : Life Histories of North American Birds, with special reference to 

 their breeding habits and eggs, 12 lith., plates Washington, 1892. (U. S. Nat. Mas.) 

 Special Bull. No. 1. The author of this superb work promises to produce in the 

 future similar volumes treating of other groups of our birds. Those dealt with in 

 the present installment are the gallinaceous birds, the Pigeons, and Birds of Prey, 

 in which latter group he includes the somewhat heterogeneous assemblage of the 

 American Vultures, the Falconidw, and the Owls. 



