g others (nine in all) to the
following conclusions:

"First, that the unsymmetrical spiral forms of the shells of these
and of all the Mollusca probably resulted from the action of the
laws of heredity, modified by gravitation.

"Second, that there are many characteristics in these shells and in
other groups, which are due solely to the uniform action of the
physical influence of the immediate surroundings, varying with every
change of locality, but constant and uniform within each locality.

"Third, that the Darwinian law of Natural Selection does not explain
these relations, but applies only to the first stages in the
establishment of the differences between forms or species in the
same locality. That its office is to fix these in the organization
and bring them within the reach of the laws of heredity."

These views we find reiterated in his later palaeontological papers.
Hyatt's views on acceleration were adopted by Neumayr.[211] Waagen,[212]
from his studies on the Jurassic cephalopods, concludes that the factors
in the evolution of these forms were changes in external conditions,
geographical isolation, competition, and that the fundamental law was
not that of Darwin, but "the law of development." Hyatt has also shown
that at first evolution was rapid. "The evolution is a purely mechanical
problem in which the action of the habitat is the working agent of all
the major changes; first acting upon the adult stages, as a rule, and
then through heredity upon the earlier stages in successive
generations." He also shows that as the primitive forms migrated and
occupied new, before barren, areas, where they met with new conditions,
the organisms "changed their habits and structures rapidly to accord
with these new conditions."[213]

While the palaeontological facts afford complete and abundant proofs of
the modifying action of changes in the environment, Hyatt, in 1877, from
his studies on sponges,[214] shows that the origin of their endless
forms "can only be explained by the action of physical surroundings
directly working upon the organization and producing by such direct
action the modifications or common variations above described."

Mr. A. Agassiz remarks that the effect of the nature of the bottom of
the sea on sponges and rhizopods "is an all-important factor in
modifying the organism."[215]

While Hyatt's studies were chiefly on the ammonites, molluscs, and
existing sponges, Cope