ALPHEUS HYATT : MEMORIAL MEETING. 
423 
factors, of the effects of migration and geographical isolation such 
as are known to take place at the present day, and from a study of 
these subjects he was led to consider how the orders of cephalopods 
originated. 
He showed that the efforts of the primitive straight-shelled nauti- 
loid (Orthoceras) “to adapt itself fully to the requirements of a 
mixed habitat of swimming and crawling gave rise to the Nauti- 
loidea; the efforts of the same type to become completely a littoral 
crawler evolved the Ammonoidea. . . We cannot,” he says, “ seri¬ 
ously imagine these changes to have resulted from intelligent effort; 
but we can, with Lamarck and Cope, picture them as due to efforts 
on the part of the animal to take up new quarters in its environment 
and then acquire habits and structures suitable to the changed 
physical requirements of its surroundings, and this position is better 
supported by facts than any other hypothesis.” 
A most interesting problem is the origin of the spiral shell of the 
snail-like molluscs. Hyatt was the first, we believe, to point out 
the obvious correlation between the gradual coiling of the shell and 
the habit of crawling or gliding. He shows that those gastropod 
shells which degenerate and tend to lose the spiral mode of growth 
and become irregularly straightened out in their older stages of 
growth, are forms which become attached or which lead sedentary 
lives. He points out the tendency in the descendants of straight 
shells (Orthoceras, etc.) to become, as the result of assuming reptant 
habits, first arcuate and then coiled, these being acquired characters 
which have been “introduced late in the ontogeny and gradually 
forced back to younger and younger stages in successive genera¬ 
tions, or species, or genera.” He also accounts for the peculiar 
horizontal or peripheral growth of the oyster, the scallop, etc., by 
their fixed or partly sedentary mode of life. 
His most peculiar investigation, and one which brought into play 
his characteristics as a patient analytic student of facts and as a 
synthetic philosopher, was what he was fond of calling his “ old age 
theory.” The idea was suggested by D’Orbigny in his early studies 
on the ammonites; and it is a most striking and captivating one, 
being exemplified in other groups of animals than the molluscs. We 
all know that in molluscs, as well as trilobites and crustaceans, dur¬ 
ing the evolution of the type, the earliest stages are simple, unorna¬ 
mented, generalized forms, which eventually give rise to those which 
