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THE AMERICAN NATURALIST [Vol. XLVII 



a school of evolutionary research. A leader in this 

 school was the late Charles Emerson Beecher, an emi- 

 nent professor in Yale University. I wish to point out 

 briefly what these principles are, and their application, 

 but without going into the question of who first enun- 

 ciated the principles, which is often difficult to ascertain. 

 For the present purpose it is sufficient to consider them 

 as the principles that Hyatt made use of and welded into 

 a component whole for phylogenetic investigation. 



It was my privilege to be intimately associated with 

 Professor Hyatt as a student and assistant from 1886, 

 until his death, in 1902, and I can not too strongly ex- 

 press the help and pleasure derived from his boundless 

 enthusiasm, ever ready sympathy and wise counsel. He 

 was laborious and painstaking in his work, constantly 

 urged the importance of large series of individuals for 

 study, and the importance of the bearing of abnormal or 

 pathological specimens. The value of a specimen to him 

 was for what it showed, by itself, and in its relation to 

 associated forms. He urged the comparative study of 

 young and adult, living and fossil forms in a united 

 study. To a zoologist the only difference that should be 

 recognized between living and fossil animals is the con- 

 dition of preservation and the time element. A study 

 of the recent throws light upon the fossil, and conversely 

 a study of the fossil throws light upon the recent. A 

 united study of both recent and fossil gives a grasp upon 

 a group that can not be attained from either alone. 



Stages in development were constantly uppermost in 

 Professor Hyatt's mind, not stages in the embryo only, 

 which are the main conception of stages to most zoolo- 

 gists, but stages throughout the life of the individual, 

 from the egg to the adult and old age. It was the later, 

 or postembryonic, stages that he especially urged the 

 importance of to the phylogenist, and he demonstrated 

 that these later stages possess characters which are 

 directly comparable to the adult condition of related 

 forms. In other words, that the ontogeny of the indi- 



