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zusammenhangenden Formveranderungen des Ammonitentieres sind 

 als senile Charaktere aufzufassen." 



I am not prepared to adopt without more extended study the first 

 of Dr. Pompeckj's results. Although he has presented very strong 

 evidence, it is difficult to believe that in all cases when the aper- 

 ture is contracted and the whorl or living chamber is excentric that 

 this is never resorbed, because these so often occur in very small 

 shells. These small shells are apparently of the same species with 

 larger ones having similar chambers, and I have certainly considered 

 them as individuals which had inherited the degenerative tendency 

 to excentricity in their early stages. Dwarfs certainly occur having 

 prematurely degenerative characters of this kind, and it may be that 

 Dr. Pompeckj is right in his generalization, and that all such occur- 

 rences can be regarded in the same way. 



Dr. Pompeckj does not deny that, when change of habit might 

 be such as to favor the inheritance of gerontic characters, that they 

 become genetic and that degenerative series might have been thus 

 built up. If this occur at all the appearance of gerontic characters 

 must take place according to the law of tachygenesis and in conse- 

 quence of this appear earlier in the ontogeny of descendants of the 

 same series. The shells in every degenerate series, therefore, ought 

 to show this earlier inheritance in proportion to their degeneracy 

 and to their place in the evolution of the series. In other words 

 some at least of the more degenerate species would necessarily 

 exhibit phylogerontic characters in their neanic stage and should 

 be classified not as dwarfs but as young shells. 



Through the kindness of Dr. C. E. Beecher my attention has 

 been drawn to a species which is of importance in this connection 

 and this has been loaned me by Prof. O. C. Marsh, Director of 

 Yale University Museum. This extraordinary helicoidal shell, 

 Emperoceras Beecheri, is exceptional in so far as it exhibits, in a 

 magnified and unmistakable way, the action of tachygenesis upon 

 gerontic characteristics. 



The neanic stage has a single, straight, baculites-like cone which 

 turns in the same plane, building out the peculiar form known as 

 Hamites. This, after making the hamitean bend, deviates from 

 the plane of growth of the neanic stage and becomes a loose but 

 regular spiral which has generally heretofore been described as 

 Helicoceras. 



