1868. | Darwin and Pangenesis. 299 
showing that when animals are first subjected to captivity, even in 
their native land, and although allowed much hberty, their repro- 
ductive functions are often greatly impaired or quite annulled ;” * 
but, on the other hand, crosses between varieties slightly modified 
render the offspring rather more fertile than otherwise. Now he 
believes that what occurs under domestication by a leap, is slowly 
proceeding in nature; for natura non facit saltwm, and that infer- 
tility has been gradually proceeding from changed conditions of 
existence, extending over long ages, but resulting at length in as 
marked a difference as when the conditions have been suddenly 
changed from freedom to captivity. 1 
But here, again, whilst the author's results appear to be cor- 
rectly stated, the parallel by which he seeks to explain the cause is 
unfortunate and inapplicable; for in the case of domestication a 
male and female of the same variety (or one of them) are suddenly 
rendered quite infertile, their “fertility becomes at once quite 
annulled ;” whereas in nature the individuals of the same species 
remain quite fertile, inter se, whilst it is only when they come to 
be crossed with other species that the union is barren. 
But there is still another aspect of the question, im which a 
simple statement of facts alone gives to the theory of modification 
a large amount of weight. 
In seeking to show that the barrier of hybridism is not so for- 
midable as his antagonists would make it appear, the author says: 
“The sterility of distinct species when first united, and that of 
their hybrid offspring, graduates by an almost infinite number of 
steps, from zero, when the ovule is never impregnated and a seed 
capsule is never formed, up to complete fertility. We can only 
escape the conclusion that some species are fully fertile when 
crossed, by determining to designate as varieties all the forms which 
are quite fertile. This high degree of fertility is, however, rare. 
Nevertheless, plants which have been exposed to unnatural conditions 
sometimes become modified in so peculiar a manner that they are 
much more fertile when crossed by a distinct species than when 
fertilized by their own pollen. Success in effecting a first union 
between species and the fertility of their hybrids depends in an 
eminent degree on the conditions of life being favourable. The 
innate sterility of hybrids of the same parentage and raised from 
the same seed-capsule often differs much in degree.” 
In our notice of the author’s former work we charged him with 
making light of the difficulties of hybridism. ‘The fact is, he was 
already in possession of a mass of information which justified his 
giving less weight to that phase of the question than we were dis- 
posed to do, for, in common with many other critics, we had been 
* « Animals and Plants under Domestication,’ vol. ii., p. 176 
+ Ibid., p. 179. 
