724 ALPHEUS HYATT. 



1. The extraordinary modifications and series of shells found at Stein- 

 heim are in one way exceptional, and owe their existence to exceptional 

 conditions. 



2. These conditions appear to he the isolation of the modified descend- 

 ants of Planorbis laevis, due to the absence of competing types and the 

 character of the environment. 



Besides other conclusions, he points out that in these and other series 

 of animals which he had studied, "in a given number of generations 

 inherited characteristics of every kind tend to appear in the descendants 

 at earlier stages than that at which they first occurred in the ancestral 

 forms." 



These studies led him to explain the frequent occurrence of parallel 

 forms, or, as they are now called, cases of convergence, also to examine 

 into the causes of senescence, of geological extinction, etc. He main- 

 tained that there was no such thing as indefinite variation, and took 

 strong ground, based on extended series of paleontological data, as to the 

 reality of use-inheritance. In this as well as his other memoirs he insists 

 on the inadequacy of natural selection in causing variation and the 

 formation of new groups. 



In a later work, entitled " Phylogeny of an Acquired Characteristic," * 

 Hyatt is at his best. The results of a life-long study of the genetic 

 series of Cephalopods, of their rise, culmination, decay or senile features, 

 and their final extinction, are portrayed in a masterly way. His conclu- 

 sions are based on the careful detailed survey of a multitude of facts, and 

 the story he unravels from the series upon series of fossil forms which 

 passed in review before eyes so well trained, and a mind so skilled in 

 induction and deduction, forms a chapter in the history of organic evolu- 

 tion which will remain a classic. 



It was only after long years of research, and the most patient, thought- 

 ful reflection on the series of facts he independently worked out, by his 

 study of the embryology of the protoconch and conch of the Orthocera- 

 tites, and their successors the Nautiloids and Ammonoids, that he thus 

 describes the gross results in a few sentences which show the mode of 

 origin of new orders through the Lamarckian factors of effort and use. 

 In this essay Hyatt struck the keynote to the cause of the origin of 

 new types, or class and ordinal forms, i. e. by the changes in habits, and 

 efforts of the organism to adapt itself to such new conditions of existence. 



* Phylogeny of an Acquired Characteristic. Proc. Amer. Phil. Soc, XXXII. 

 p. 371 (1894). 



