Geology and Natural History. | 327 
“I propose, in the last place, briefl sia 
th a ast place, briefly to examine the bearing of 
on case of ‘ descent with modification,’ which I cas 
ny athe sp dae the general ‘Theory of Descent’ and of the 
“ - 
“ahaa spa ais in ‘natural selection’ or the ‘survival of the 
ssoameit “sufficient explanation of the ‘origin of species,” 
from ; 
self. seas the fundamental question is (as Mr. Darwin bim- 
mens ei = at any rate in his later years), what gives rise to 
ep saad “ exercise of ‘natural selection’ could produce 
ve changes presented in the evolutionary history of 
nal. ‘ : 
ine middle-sized O. duplex and a small 0. complanata, 
without the the trained eye of the naturalist canno distinguish 
iy € assistance of a magnifying-glass. 
) 
selectj a 
ton’ can give no account of either the origin or the perpetu- 
Orbitolites complanata. 
‘ series a 
to exclude the notion of ‘casual’ 
codic cor ss it ; : 
= eyo of a-young Cornuspira, and the discoidal body of an 
€, with its thousands of sub-segments disposed with the 
and unifor i i 
eat modes, who (in the absence of the intervening links) 
ean suspected any genetic relatio 
to construct a pedigree? And yet : 
from 
sieni ety one to the other to be not only most complete, but often 
as se cant of further progress; many of the changes being such 
ont, Dave: 8 i ticipations of greater 
penta o meaning except as an 
ges to come. Thus, the slight constrictions that show them- 
