615 
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 toa 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. 
