A tendency to sudden reversions to the perfect character of either parent would, also, be much more likely to occur with mongrels, which are descended from varieties often suddenly produced and semi-monstrous in character, than with hybrids, which are descended from species slowly and naturally produced.

On the whole, I entirely agree with Dr.Prosper Lucas, who, after arranging an enormous body of facts with respect to animals, comes to the conclusion that the laws of resemblance of the child to its parents are the same, whether the two parents differ little or much from each other, namely, in the union of individuals of the same variety, or of different varieties, or of distinct species.
Independently of the question of fertility and sterility, in all other respects there seems to be a general and close similarity in the offspring of crossed species, and of crossed varieties.

If we look at species as having been specially created, and at varieties as having been produced by secondary laws, this similarity would be an astonishing fact.

But it harmonises perfectly with the view that there is no essential distinction between species and varieties.
SUMMARY OF CHAPTER.
First crosses between forms, sufficiently distinct to be ranked as species, and their hybrids, are very generally, but not universally, sterile.

The sterility is of all degrees, and is often so slight that the most careful experimentalists have arrived at diametrically opposite conclusions in ranking forms by this test.