ALPHEUS HYATT. 721 



called Haeckel's " biogenetic law," runs through and is the motif of 

 Hyatt's life-long work. 



Some of us in our maturer years return to or continue to work along 

 the lines taken up in youth. Hyatt for a period of forty years, in a series 

 of profound studies on the Cephalopods, in publications rich in exact ob- 

 servations and with ample illustrations, many of the drawings beautifully 

 executed by his own hand, independently expanded and illustrated this 

 fundamental phase of evolution, which so impressed him in his student 

 days. 



His remarkable memoir on the " Genesis of the Arietidae," published 

 in 1889 in the Smithsonian " Contributions to Knowledge," and jointly 

 with the Museum of Comparative Zoology, is a storehouse of facts on 

 which his generalizations are based. When he presented his views to 

 the National Academy of Science at a Washington meeting, Professor 

 Henry expressed his approbation of the value and profoundity of this 

 research. In this work he insists on his law of Morphogenesis, i. e., 

 he attempts to demonstrate that " a natural classification may be made 

 by means of a system of analysis in which the individual is the unit 

 of comparison, because its life in all its phases, morphological and physi- 

 ological, healthy or pathological, embryo, larva, adolescent, adult, and 

 old (ontogeny), correlates with the morphological and physiological his- 

 tory of the group to which it belongs (phylogeny)." 



In the beginning of his studies, contemporaneously with Cope, he 

 insisted on the fact and results of a process of acceleration and re- 

 tardation and the growth of the individual as well as the evolution of 

 the family, order, or class of which it was a member. 



" All modifications and variations," he says, " in progressive series 

 tend to appear first in the adolescent or adult stages of growth, and then 

 to be inherited in successive descendants at earlier and earlier stages ac- 

 cording to the law of acceleration, until they either become embryonic, 

 or are crowded out of the organization, and replaced in the development 

 by characteristics of later origin." 



Another of the nineteen conclusions prefacing this essay is No. 14 : — 



" The law of acceleration in development seems, therefore, to express 

 an invariable mode of action of heredity, in the earlier reproduction of 

 hereditary characteristics of all kinds and under all conditions. In pro- 

 gressive series it acts upon healthy characteristics, and appears to be an 

 adaptation to favorable surrouixlings, and in retrogressive series upon 

 pathological characteristics, and is probably an adaptation to unfavorable 

 surroundings, usually leading to the extinction of the series or types." 



v<ii,. xxxvni. — -JO 



