MEMOIR OF ALPHEUS HYATT 507 



rather than to the Darwinian — evolution through the use and disuse of 

 parts and other Lamarckian factors appealing to him more strongly than 

 evolution through natural selection. 



Some of his most important theories were, however, first fully worked 

 out and illustrated in the memoir on the genesis of the Tertiary species 

 of Planorbis at Steinheim. This investigation led him to Steinheim, 

 where he made an exhaustive study of these shells as they occur in the 

 successive strata of fresh water lakes, and, as perhaps the most striking 

 result, he was enabled to demonstrate that — 



" a single species, finding itself in an unoccupied field, proceeded with unexampled 

 rapidity to fill it by the evolution of new species and many forms, all differing 

 from each other, but all referable by intermediate varieties to the original type." 



But the ammonites afforded Professor Hyatt material especially 

 adapted to the kind of work in which he most delighted. In this mar- 

 velous group he worked out the correlation between the development of 

 the individual and that of its class. In the span of life of a single crea- 

 ture he read the history of the race. This group also afforded a basis 

 for his demonstration that new characteristics are acquired in response 

 to the demand of necessity, and that these acquired characteristics are 

 inherited at earlier and earlier stages in successive generations, thus ac- 

 celerating the development of the race. These points are developed in 

 a masterly manner in his paper on the phylogeny of an acquired char- 

 acteristic, and oppose successfully the view that acquired characters can 

 not be inherited. 



Professor Hyatt not only recognized the successive stages in the life 

 history of the individual and correlated them with the adult stages of 

 ancestral groups, but he devised a complete nomenclature for these 

 stages, which has gained general acceptance. The law of acceleration 

 of development, known as the law of tachygenesis, and affording the key 

 to the complex problems of phylogeny, was discovered almost simul- 

 taneously, but quite independently, by H^^att and Cope in 1866, and in 

 all his subsequent writings Hyatt was more than just in his cordial 

 recognition of Cope's claim, finding, with the utter lack of jealousy 

 which was one of his most i:>rominent traits, additional gratification in 

 the coincidence which made these two eminent collaborators warm 

 friends for the rest of their lives. This great principle was rediscovered 

 some years, later by Wiirtenberger, and that it should come to be gen- 

 erall}^ known abroad as Wiirtenberger's law could not naturally be re- 

 garded with quite the same degree of equanimity, although Professor 

 Hyatt never doubted that time would right the error. 



