1912] The Ottawa Naturalist. 39 



the identity of changing structures under the disguise of new 

 forms, but to measure the rate of these changes, and to seek 

 out the underlying causes that have brought them about. He is 

 heavily handicapped by the lack of materials that can be pre- 

 cisely measured or controlled. But on the other hand there is a 

 certain advantage inherent in the very size and remoteness of 

 his problems, that is absent in the brief laboratory experiments 

 that have taken place under the eye of man. His problems must 

 be viewed from a great distance, but one that gives a large 

 perspective, and draws a vast range of structural changes into 

 a single horizon w^here sporadic details disappear, and only those 

 events catch the eye that are massed around some central cause 

 or are ranged with monotonotis regularity along some common 

 line of physiological upheaval." 



Whether or not the reader accepts all the author's con- 

 clusions, there can be only the greatest admiration for the work 

 that has preceded the writing of this important book, as well 

 as for the marked ability with which the arachnid theory is 

 presented. The work is a masterpiece, and marks an important 

 step in the progress of zoologv. 



The publishers, P. Blakiston's Son & Co., are to be com- 

 plimented upon the excellent get-up of the volume. The press 

 work is very fine. J. M. S. 



A History of the Birds of Colorado, by William Lutlev 

 Sclater, M.A. (Oxon.), M.B.O.U., Hon. M.A.O.U., (lately 

 Director of the Colorado College Museum), with seventeen plates 

 and a map; Witherbv & Co., 326 High Holborn, London; price 

 $5.00. 



This new volume of 576 pages is founded upon the very 

 complete collection of Colorado birds formed, during the last 

 thirty-five years, by Mr. Charles E. Aiken, of Colorado Springs. 

 The number of Colorado birds included is 392, and of these 

 22 5 are considered as regular breeders within the State. The 

 nomenclature and classification used are almost without excep- 

 tion that of the recently published third edition of the A. O. U. 

 check list. 



Under each species is given references to Colorado Records', 

 Descriptions of the Adults, Distribution and Habits, which latter 

 includes nesting habits with an account of the eggs. Pages 533 

 to 551 are devoted to a Bibliography which includes references 

 to all articles on Colorado ornithology of importance, up to 

 December, 1910. 



Students of birds generally will welcome this important 

 contribution to American ornithology. There is no apology 

 necessary for the appearance of this additional bird treatise. 



