396 REVIEWS— ON THE ORIGIN OF SPECIES. 
bility, and what proof can be brought forward of the tendency of long 
periods of time, to change the characters of species. 
Atavism is but a name for the general law that the offspring re- 
semble the parents. The resemblance is not a complete and exact 
one, but it is real and certain, and we believe it to include all the par- 
ticulars which characterise the species. There is a certain amount of 
variation arising partly from assignable, partly from unknown causes, 
the nature and extent of which is learned by experience. In cases of © 
a sexual reproduction, whether naturally occurring by gemmation or 
fissure, or artificially produced by section with replacement of parts, . 
the variation. is almost nothing. In reproduction by the fertilised 
ovum a regular series of changes is passed through before reach- 
ing the complete condition of the organism, and this condition is not 
an exact copy in every particular of the parents, for they themselves 
differ in some points; there are variations in the influence of each 
parent upon the offspring ; there are effects of such causes as tempera-- 
ture, food, atmospheric conditions, and superinduced habits on the- 
development of the germ; and there are internal causes not to be 
estimated by us which, within seemingly narrow limits, affect develop-- 
ment so as to produce slight deviations from a precise pattern. Again. 
it is observed that existing varieties in parents are most commonly 
transmitted to the offspring, if found alike in both parents very gene-- 
rally ; if only occurring m one parent, much less uniformly, yet the- 
peculiarity frequently occurring. When by selective breeding a variety 
is kept up through successive generations, it becomes a permanent. 
variety or race which may either have become insulated by its position: 
or may be studiously kept up on account of its beauty or utility, but if 
the causes which maintain the variety are removed the offspring 
gradually return to the more normal specific types. The advocate of 
the Darwinian hypothesis believes that no real difference can be re-- 
cognised between species and varieties; that there are no determinate 
inherent tendencies of development limiting the action of causes of” 
variation, and that new species are produced, as some also become ex-. 
tinct, in the ordinary course of nature. We ask, has he proved by 
sufficient examples that varieties tend to recede more and more from. 
the specific type and do not tend to return to it; that species are 
capable of mixing by the production of fertile intermediate forms 
which thus in reality become new species, or that palzeontological. 
facts encourage the idea, that species are transmuted, of course very. 
