794 Recent Literature. 3 [ October, 
can naturalists, have resulted in a distinctive American school of 
evolutionists, if we may venture so to style it. Cope and Hyatt each 
working quite independently of the other, and in different branches 
of the animal kingdom, have arrived at the conclusion that spe- 
cies and genera may be both slowly, and sometimes suddenly 
produced through the action of the environment upon the animal 
or plant, producing a tendency to variation, after which the action 
of the laws of heredity, checked by natural selection, legitimately 
produced their results. 
It is not our present purpose to make an exposition of Cope and 
Hyatt’s views, but referring the reader to their essays and articles, 
to give in this review the results of Professor Hyatt’s studies on 
the evolution of the Steinheim fossil snail-shells. These Tertiary 
fresh water shells occur in great abundance and variety of form 
and individuals in clay pits at Steinheim, near Stuttgartt. The 
shells lived ina Miocene pond or lake more or less shut in from any 
other waters. Attention was first called in 1866, in a brief papet 
by Dr. Hilgendorf, to the shells in these beds, and the light they 
threw upon the evolution theory, which led Professor Hyatt, 
1872, to collect these shells in large numbers, and to make an 1- 
dependent examination of them. The shells all belong to the 
genus Planorbis, and the numberless varieties and forms taken 
from the beds, appear to be lineal descendants of four varieties of 
a single ancestral species (Vanorbis devis ), found in the lowermost 
beds deposited at the bottom of the Jake. The inhabitants of 
these beds were not necessarily evolved through a vast period of 
time (as in general demanded by Darwinians) but Hyatt states 
that Professor Cope’s researches among fishes and reptiles, his 
own among Ammonites, and at a later date Mivart’s work on ~ 
“ Genesis of Species,” have all given a large amount of evidence, 
which tends to the conclusion “that vast periods of time are not 
necessarily essential to the production of new species, OF cues 
new generic or family forms,” 
t considers that the normal, smooth, primordial form 
(Planorbis levis) lived in neighboring Miocene lakes, and, before 
its migrations into the Steinheim lake, had four varieties, and 
subsequently reproduced these or their immediate descendants in 
the Steinheim lake. Four principal series were developed from 
these four varieties after their migration into the Steinhet 
and while the original forms in the first series or line of descent 
had the closest relationship with each other, their descendants 
gradually diverged, until finally no hybrids connected the differ- 
ent series with each other. The first series culminated in vari 
