418 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
forms of life were built! I do not say we know enough to make it 
certain it is so, but I do not see why they are not features upon 
which life itself is built.” Hyatt was at this time working on the 
fresh-water mussels of North America. He had collected a large 
amount of material from the Ohio and other rivers and was hard at 
work on the anatomy and classification of the family. After this 
lecture he turned has attention to the ammonites, and his first paper, 
read before the Agassiz zoological club, March 22d, 1860, was on the 
ammonites of the Jura, and in that paper he began a series of 
investigations which only ended with his life. His various memoirs 
on this subject were published by the Boston society of natural 
history and the Museum of comparative zoology. His very exten¬ 
sive memoir, published in cooperation with the Museum of compara¬ 
tive zoology, on the Genesis of the Arietidae formed one of the 
Smithsonian contributions to knowledge. 
My task would have been easier had I been asked to analyze the 
man through his works. This task, however, has been assigned to 
others, yet I cannot refrain from calling attention to the extent and 
diversity of his works as shown in the very numerous communica¬ 
tions to scientific societies. A study of these memoirs shows a unity 
of purpose and a continuity of thought which, considering their 
extent over forty years of time, is somewhat remarkable. Many of 
these memoirs were beautifully illustrated by their author, whose 
artistic and accurate pencil aided greatly in making clearer the 
somewhat abstruse principles involved in his studies. It seems a 
wide jump from the study of fossil cephalopods to living fresh-water 
Polyzoa, yet it is easy to explain. Agassiz had so impressed us 
with the classification of Cuvier that we never doubted the exist¬ 
ence of four great plans of structure in the animal kingdom. 
Indeed nothing could be plainer than the radiate type, the articulate 
type, and the vertebrate type; the molluscan type was not so clear 
in our minds. We could follow out the homologies of the three 
higher classes of Mollusca, but precisely how the Polyzoa and 
Brachiopoda came under the same category was a serious difficulty 
in the way of that conformity so apparent in the other branches. I 
have always felt that Hyatt was first led to the study of the Polyzoa, 
the results of which were finally published by the Essex institute, 
simply to make clear the molluscan affinities which were supposed 
to exist. I know that my attention was first drawn to the Brachio- 
