The majority of these eggs had been fertilized, and in the majority of the fertilized eggs the embryos either had been partially developed and had then aborted, or had become nearly mature, but the young chickens had been unable to break through the shell.

Of the chickens which were born, more than four-fifths died within the first few days, or at latest weeks, 'without any obvious cause, apparently from mere inability to live,' so that from 500 eggs only twelve chickens were reared.
The early death of hybrid embryos probably occurs in like manner with plants, at least it is known that hybrids raised from very distinct species are sometimes weak and dwarfed, and perish at an early age, of which fact Max Wichura has recently given some striking cases with hybrid willows." Mr.Darwin objects to the notion that there is any special sterility imposed to check specific intermixture and change, saying,[123] "To grant to species the special power of producing hybrids, and then to stop {125} their further propagation by different degrees of sterility, not strictly related to the facility of the first union between their parents, seems a strange arrangement." But this only amounts to saying that the author himself would not have so acted had he been the Creator.

A "strange arrangement" must be admitted anyhow, and all who acknowledge teleology at all, must admit that the strange arrangement was designed.

Mr.Darwin says, as to the sterility of species, that the cause lies exclusively in their sexual constitution; but all that need be affirmed is that sterility is brought about somehow, and it is undeniable that "crossing" _is_ checked.

All that is contended for is that there _is_ a bar to the intermixture of _species_, but not of _breeds_; and if the conditions of the generative products are that bar, it is enough for the argument, no special kind of barring action being contended for.
He, however, attempts to account for the modification of the sexual products of species as compared with those of varieties, by the exposure of the former to more uniform conditions during longer periods of time than those to which varieties are exposed, and that as wild animals, when captured, are often rendered sterile by captivity, so the influence of union with another species may produce a similar effect.