REVIEWS—ON THE ORIGIN OF SPECIES. 397 
_ gradually, through a lengthened period of time? The transmission 
through several generations of the monstrosity of a sixth finger, has 
no more to do with specific distinctions than the transmission of a 
particular cast of features, complexion, tendency to certain diseases or 
any similar instance of atavism acting in subservience to the more 
marked tendencies which constitute species. The history of the otter 
breed of sheep exemplifies the formation and preservation of races, but 
affords no argument for their breaking through the natural boundaries 
-of species. The case of the varieties of pigeons is a very interesting 
one, and the more so because the leading varieties seem to exhibit the 
same tendencies of development which distinguish the larger really 
distinct groups and prevail throughout nature; but so long as it is 
-generally agreed that all the varieties have sprung from columba livia, 
-and it is reasonably supposed that if not under the care of man they 
‘would gradually fall back into that species, instances of partial return 
being frequent ; and so long as the difficulty remains, which is can- 
didly acknowledged by Prof. Huxley, respecting the general if not 
universal infertility of hybrids between species, we cannot admit 
that the phenomena of the races of domestic pigeons afford any evi- 
dence whatever against the natural and real separation of species. 
‘Races which are habigually under the care of man, being cherished 
and kept in favourable circumstances to suit his purpose, may well 
illustrate the extent to which variations may be carried, but are least 
of all to be alleged as examples of the formation of distinct types of 
structure, the very fact of the peculiarities occurring in such circum- 
stances being a warning to us against attributing to them any specific 
importance. 
We have such clear evidence of the antiquity of various existing 
species both of animals and plants, which plainly appear to be now 
what they were many centuries ago, that the presumption is against 
the influence of time in modifying organised structures. Direct evi- 
dence on the subject can only be derived from palaeontological studies, 
_and the defenders of the Darwinian hypothesis have been forward to 
claim the facts of the paleontology as favouring their views. The 
following passage from Mr. Huxley shows how they proceed: (Lect: 
VI., p. 136—140, Am. Ed.) 
“If you regard the whole series of stratified rocks—that enormous thickness 
of sixty or seventy thousand feet that I ave mentioned before, constituting the 
only record we have of a most prodigious lapse of time, that time being, in all 
_ Probability, but a fraction of that of which we have no record ;—if you observe 
