Botany. 447 
forms, as Oliva, Mitra, Triton, dentbinlats te ie n the earlier period, 
have come into view in the latter. But let it be prise) What follows ? 
These small differences then, accomplished in all that prodigious range o 
elapsed time, under all that variety of physical changes and removals, 
eT ee eee 
tem, deposited within the same grand period, and under much similarity 
of conditions, argue a facility in giving variations: let this operation be 
supposed to be continued in the interval between the epoch of Stonesfield 
and 4 of Australia, and the effects summed by natural selection, the 
result is the modern eovige scarcely differing more iu appearance from 
they differ one another. But, if not so deri 
ea fossil fesse than i from er 
] descent, but ng epara temporaneous 
j bia or on of life, how should it happen that plants and quad- 
rupeds on land and mollusks in the sea, should in each of these two ¢ 
for several similar sac ms in similar associations, fit with the Sport of 
continual developme 
‘This is neatly ae But it seems to be founded on the supposition a 
| variation in descent is somehow caused by time and change, and goes on 
3 by something like sia increments in equal times ; whereas, the cause at 
variation is wholly occult,—the fact is, that some forms remain long inva- 
riable or slightly variable under the same conditions in which others vary 
wr If Mr. Darwin’s theory is bound to explain variation, or to assign 
reason for one species varying when another does not, then it —— 
fails, for it can do no such thing. If, seated: it does not unde 
account for the diversity of species except by regarding — as vaftebes 
of earlier origin and wider divergence,—leaving the reaso why tke pro- 
geny is sometimes unlike the parent in one or more partic ieclans as much 
: unexplained as why it is usually like it, ~ showing how the struggle for 
lite ensures the extinction of crow termediate forms, and now the 
resulting natural selection may lead ona surviving races farther raed 
the lines of favorable variation,—then it avoids the force of many of the 
a which have been directed against it. 
uR. Sc1.—Szconp Serres, Vou. XXXI, No. 93.—Mar, 1861. 
58 
