COMPARATIVE OOLOGY OF NORTH AMERICAN BIRDS. 193 



forms and to the measurements of eggs. In regard to the last, or the 

 measurements of eggs, it is a matter of the very, highesl importance to 

 the avian oologist. Throughout the present paper I have frequently, 

 but not always, contrasted the measurements as given ns by different 

 authorities, and it will be seen that the variance in statements in this 

 particular is often quite as great as are the descriptions of form and 

 color. The fact is the eggs themselves of the same species vary greatly 

 in size, and averages taken from large series constitutes the only kind 

 of data that can be safely relied upon. Nests and their environments 

 are deserving of the most painstaking studies and descriptions, and 

 frequent comparisons should be made of the nests of birds of allied 

 families and groups. The best oological works are those which are 

 fully illustrated with the most correct colored tignres of eggs. In many 

 instances a full knowledge of the breeding habits, nesting, and oology 

 of birds will be of powerful assistance in determining the affinities of 

 avian types. From a scientific standpoint avian oology has accom- 

 plished much in the past and will undoubtedly do so in the future. 



