ALPHEUS HYATT. 723 



of descent. His 1866 paper on "Parallelism," etc., was in this same 

 vein of thought, but in this paper, conceived along evolutional lines, he 

 did not explicitly state what were the actual dynamic agencies at work to 

 produce the transformation from one form to another. His studies on the 

 geological succession of the Ammonites, and the obvious genetic relations 

 of the series he examined afterwards, naturally led him to adopt such 

 views. 



He claimed in this paper that the reversionary species he examined 

 " all descended from one." In 1873 he showed that in the Ammonoids 

 there are everywhere instances of the slow accumulation of differences, 

 according with the Darwinian method, and of their quick and sudden 

 production, "according to the law of acceleration as explained by Cope 

 and the writer, and subsequently by Mivart." * 



His Lamarckian leanings, however, so far as his published works show, 

 crop out in his " Abstract of a Memoir on the Biological Relations of the 

 Jurassic Ammonites." f The stages of growth he describes are here 

 directly attributed to the favorable nature of the physical surroundings, 

 primarily producing characteristic changes which become perpetuated and 

 increased by inheritance within the groups. The production of retro- 

 gressive, senile forms he attributes to " the action of unfavorable sur- 

 roundings." He carefully guards against " attributing the origin of these 

 differences to the law of natural selection," limiting the action of this 

 law " strictly to the modification of the structural differences which tend 

 to appear first in the varieties and then by inheritance in larger and 

 larger groups and at earlier and earlier stages in the life of the individual." 



Hyatt's beautiful research on the problems suggested by the fossil pond- 

 snails of Steinheim near Stuttgart, Germany, is an important contribution 

 both to paleontology and to evolutional data. Hilgendorf had previously 

 (in 18GG) described the conditions, and his results were regarded in 

 Germany as amouutiiisr to a demonstration of tlie truth of the evolution 

 theory. Hyatt, during a year's residence in 1872 near Stuttgart, spent 

 five weeks examining the pits and made careful collections. 



The discussion is a most valuable contribution to the theory of descent. 

 Sir Richard Owen wrote him in 1881 : "I cannot say more than tliat I 

 deem it a model of the way and aim in and by whicrh such researches 

 should be conducted in the present phase of Biology." 



Hyatt's patient and loi'g sustained studies led him to the following 

 conclusions: 



* Proceedings Boston Soc. Nat. Hist , XVI. p 107. Dec. 3, 1873. 

 t Ibi.l, XVII. pp. 230-211. Dec. 10, 1874. 



