378 REVIEWS—ON THE ORIGIN OF SPECIES. 
produced and the old ones acting and reacting oneach other. Sv that in any one 
region and at any one time, we ought only to see a few species presenting slight 
modifications of structure in some degree permanent; and this assuredly we see. 
Secondly, areas now continuous must often have existed within the recent period 
in isolated portions, in which many forms, more especially amongst the classes 
which unite for each birth and wander much, may have separately been rendered 
sufficiently distinct to rank as representative species. In this case, intermediate 
varieties between the several representative species and their common parent, 
mnst formerly have existed in each broken portion of the land, but these links 
will have been supplanted and exterminated during the process of natural 
selection, so that they will no longer exist in a living state. 
Thirdly, when two or more varieties which have been formed in different 
portions of a strictly continuous area, intermediate varieties will, it is probable, 
at first have been formed in the intermediate zones, but they will generally have 
had ashort duration. For these intermediate varieties will, from reasons already 
assigned (namely, from what we know of the actual distribution of closely allied or 
representative species, and likewise of acknowledged varieties), exist in the 
intermediate zones in lesser numbers than the varieties which they tend to connect. 
From this cause alone the intermediate varieties will be liable to accilental 
extermination; and during the process of further modification through natural 
selection, they will almost certainly be beaten and supplanted by the forms whith 
they connect; for these, from existing in greater numbers will, in the aggregate, 
present more variation, and thus be further improved through natural selection 
aud gain further advantages. 
Lastly, looking not to any one time but to all time, if my theory be true, 
numberless intermediate varieties, linking most closely all the species of the same 
group together, must assuredly have existed; but the very process of natural 
selection constantly tends, as has been so often remarked, to exterminate the 
parent-forms and the intermediate links. Consequently evidence of their former 
existence could be found only amongst fossil remains, which are preserved, as we 
shall in a future chapter attempt to show, in anextremely imperfect and intermit- 
tent record.” 
With regard to the objections placed under the second head, 
objections of perhaps a still more grave character, the replies, as 
might be expected, are even still less satisfactory. We have here, 
indeed, two principal difficulties which it is impossible to set aside 
except by the aid of entirely gratuitous suppositions. In one of 
these difficulties, the mode of transition of one generic form into 
another—of (and Mr. Darwin might have chosen a more startling 
example) an insectivorous quadruped into a bat, for instance—the 
author confesses that he can give us no rational explanation. At 
the same time, he thinks such difficulties have very little weight. 
The arguments here, we trust we do not speak offensively, for nothing . 
