48o" REPORT OF NATIONAL MUSEUM, 1892. 



dicated by the spiral markings not uncommonly observable in the eggs 

 of some birds of prey and others — the larger end of tin 1 egix (when the 

 ends diner in form) making way for the smaller."* 



"At the same time the eggs of a great number of birds have, besides 

 these last and superimposed markings, more deeply seated stains, gen- 

 erally of a paler and often of an altogether different hue, and these are 

 evidently due to some earlier dyeing process. The peculiar tint of the 

 ground color, though commonly superficial, if not actually congenital 

 with the formation of the shell, would appear to be diffused soon after." 

 (Art. "Birds," Encycl. Brit,, 9th ed., Vol. in, p. 773.) This. distin- 

 guished ornithologist also invites attention to the fact that "the size 

 of eggs is generally but not at all constantly in proportion to that of 

 the parent. The Guillemot (Alca troile) and the Raven (Corvns corax) 

 are themselves of about equal size, Their eggs vary as ten to one." 

 (Loc. cit., p. 775.) Many other examples of this among our Ameriean 

 avifauna will be recalled by the thoughtful oologist. Reasons for these 

 discrepancies are not far to seek, i. e., nestling Ravens lay long in the 

 nest after birth, whereas young Guillemots are larger and better devel- 

 oped at the time of hatching. Then the number of eggs laid by a 

 Raven may be as many as 8 (see table), and, as we know, the Guillemot 

 lays but one, giving either bird about the same egg surface to cover 

 during incubation. 



From my reading of avian oologieal works I And that certain expla- 

 nations, or partial explanations have been put forth as the reasons for 

 the variations in the colors of the shells of birds' eggs. I formulate 

 these as follows : 



BIOLOGICAL LAWS EXPLANATORY OF THE VARIATION IN COLOR OF 

 THE SHELLS OF EGGS IN THE CLASS AVES. 



<1. In many instances the general color and markings art 1 in conform- 

 ity with the law of protective coloration. 



2. Where both sexes are more or less brilliantly colored the eggs 

 are generally laid where they are not exposed to view, and where the 

 parent hatching them is also concealed to a greater or less extent. 

 This is effected by either the form of nest constructed or by the eggs 

 being laid in burrows or hollow trees. The eggs of such birds are, as 

 a rule, not handsomely marked, or often only white. Otherwise in 

 general, irrespective of plumage, birds that lay in such places as have 

 just been mentioned usually lay white eggs. 



*That the larger end is protruded first was found on actual experiment by Mr. 

 Bartlett, superintendent of tlie gardens of the Zoological Society, to be the case 

 commonly, but as an accident the position may be sometimes reversed, and this will 

 most likely account for the occasional deposition of markings on the smaller instead 

 of the larger end, as not unfrequently shown in'eggs of the Sparrow Hawk (Accipiter 

 tiisns). The head of the chick is always found at the larger end. [For a beautiful 

 example of the heavy deposition of nearly all the color at the small end of the egg, 

 see the one figured by Beudire ofAccipiter rclox, PI. v, Fig. 17. — it. w. s.] 



