E(2) REV G) © WHIDBORNE, M.A., ON QUESTIONS INVOLVED 
which, in spite of their resemblance, are so distinct that their 
individuals can rarely be confused. It has to be remembered 
too that fine specific distinctions scientifically drawn have 
often in nature no more than varietal force, and that if by 
the conjunction of such forms the number of ac knowledged 
species were reduced, the ratio of known instances of trans- 
gression of specific limits would be very much more than 
proportionally lessened. It has to be remembered too that 
the actual tracing of a being from one species to another is a 
very different thing to the “tracing of it from one genus to 
another, and that extreme evolution no less dem ack the 
latter (and much more) than it does the former. On the 
other hand, one has only to collect a few ordinary species en 
masse to realize how strong, in spite of individual variability, 
specific unity generally is. When, for instance, Atrypa 
reticularis may be collected in vast multitudes from England, 
Germany, America, China, Australia and the Arctic regions, 
and from the Silurian and Devonian; when it varies so 
greatly within itself that two specimens are rarely fac- 
similes, and yet has so strong an individuality that there is 
as a rule little difficulty in recognizing it; and when there 
appears to be absolutely no trace of anything like it im the 
Carboniferous age*; it can only be said that specific stability 
is sometimes a very formidable opponent to the play of 
evolution. 
It may be remarked, by the way, that the force of one of 
the supposed motors of evolution—viz., Sexual Selection— 
must evidently be in the main against, and not for, variation, 
being of necessity an antidote to individual variability. 
5 (3). A kindred difficulty arises, when we attempt to trace 
the genealogy of species through successive ages. Here too 
we find much evidence in favour of evolutionary action. We 
find sometimes two species in consecutive ages, distinctly 
different,and yet so similar that it is natural to suppose that the 
one has descended from the other, although the actual linking 
may be rarely observed. But we may often go very much 
further; we often trace such nearly similar forms on thr ough 
many ages, and then their very connection becomes as much an 
argument for the limitation, as for the existence, of variation. 
From first to last their variation hardly exceeds generic 
* Unless shells described by Professor Herrick from a “ Devonian 
facies of the Waverley or earliest Carboniferous fauna of Ohio” be an 
exception. 
