COMPARATIVE OOLOGY OF NORTH AMERICAN BIRDS. 487 



3. Where the general tone of the plumage of the incubating parent 

 is- in harmony with its environment, the eggs, as a rule, are laid in 

 open nests or places where they are fully exposed to view. Such eggs 

 are frequently very handsomely tinted and marked, or the reverse may 

 he the ease. 



4. When the female alone incubates, and is of dull or somber plum- 

 age, the male bird brilliantly feathered, the third law, as a ride, is op- 

 erative. 



5. Frequently birds that lay eggs in open and exposed places, as di- 

 rectly on the ground, rock, or sand, without any apology for a nest, 

 their eggs are either tinted, or colored and marked, or both, so as to 

 be in harmony with their surroundings. 



(>. It is probable that the earliest forms of birds laid white, ellip- 

 soidal eggs, varying in number to the clutch from one to many. Pos- 

 sibly in some of the lower types of existing birds such an ancestral 

 trait has persisted. 



7. In certain instances where birds lay exposed to view either white 

 or light tinted eggs, or those not otherwise protectively colored, they 

 have the habit of covering the clutch over with leaves, etc., when, for 

 any purpose, the incubating parent temporarily quits the uest. 



8. Birds, irrespective of the character of the coloration of their 

 plumage, which habitually lay in inaccessible places, their eggs are often 

 either white or light-tinted and exposed to view. 



9. Both the age of the bird and the physical condition of its consti- 

 tution at the time of laying an egg have their influence upon the color- 

 ation of its shell. Changes in the constitution may be due to external 

 causes, as fright, etc., or to internal causes, as disease, etc. The rich- 

 est colored eggs of any species (that lay other eggs than white ones) 

 are laid by that species at its prime. 



10. The positions of the egg as it passes down the oviduct, as well as 

 its motions, effect the pattern of its markings. 



CONCLUDING REMARKS. 



In the light of what has been presented in this paper we can now 

 briefly review some of the oological peculiarities of the birds of Xorth 

 America. 



Many Grebes (Podicipoidea) have the habit of covering over their 

 numerous white eggs with bits of vegetation when the parent tempo 

 rarily quits the nest (seventh law), but whether the Loons ( Urinatoroidea) 

 ever resort to this means of protection 1 am not at present informed, 

 though I am inclined to think they do not. The eggs of the latter, how- 

 ever, harmonize better with their surroundings (fifth law). 



The American Tubinares, with but one or two exceptions, as far as 

 known, lay white eggs, but they are protected, from the fact that they 

 are laid either in inaccessible or little frequented places (eighth law). 

 Birds rather low in the scale of organization, as the Short-tailed Alba- 



