NATIONAL ACADEMY OF SCIENCES. 



A life-long friend, who was his fellow-student in the early 

 days at Cambridge, gives this account of its inception: "I have 

 always believed," he says, "that Hyatt's studies of the features 

 attending old age, and ultimately his theoiy of acceleration and 

 retardation, received its first impulse from a graphic lecture 

 given by Agassiz on the ammonites of the Jura. 



"In the upper beds of the Jura, as is well known, the ammon- 

 ites assume bizarre forms, the whorls becoming uncoiled, free, and 

 variously turned. In this lecture Agassiz, by way of metaphor, 

 compared the appearance of these ammonites to the contortions 

 and death-struggles preceding the extinction of the group. In 

 referring to these curious forms, 'It is,' said he, 'as if the con- 

 tortions of death were an idea on which the forms of life were 

 built.' " 



As is well known, Agassiz regarded a species as an idea in the 

 creative mind, independent of and superior to its manifestation 

 in material beings. The conception of the mutability of species 

 was demanding the consideration of thoughtful men at this 

 time, and the publication of Darwin's Origin of Species was 

 almost simultaneous with the publication of Agassiz's Essay on 

 Classification, which we are told that Hyatt learned by heart. 



Hyatt was influenced, as were his companions, by the new 

 view, and he seems to have sought a compromise in the concep- 

 tion that, while species change, a long series of species has a life 

 cycle like that of an individual organism, passing from the 

 infancy of its first appearance through childhood and adolescence 

 lo perfect manhood, to lapse into senility, ending in death or 

 the end of the long series of species, which is no longer repre- 

 sented by fossils in later formations. 



Hyatt believed that we have in the old-age theory an explana- 

 I ion of the way in which species arise and pass away an account 

 of the origin of species. 



In the case of the ammonites the well-known facts are these: 







The earliest forms are unornamented and their septa are simple. 



Thev are followed in geological succession by forms that are 

 ornamented with spines and tubercles, with their septa folded 

 and frilled in a way that gives to us a keen sense of their 

 elegance anil grace. In still more recent forms all these graceful 

 a.nd elegant features reach their highest perfection. J n still 



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