Origin of Species Variorum

adult: thus Owen has remarked in regard to cuttle-fish, "there is no metamorphosis; the cephalopodic character is manifested long before the parts of the embryo are completed;" and again in spiders, "there is nothing worthy to be called a metamorphosis." ↑ The larvæ of insects, whether adapted to the most diverse and active habits, or quite inactive, being fed by their parents or placed in the midst of proper nutriment, yet nearly all pass through a similar worm-like stage of development; but in some few cases, as in that of Aphis, if we look to the admirable drawings by Professor Huxley of the development of this insect, we see no trace of the vermiform stage.

How, then, can we explain these several facts in embryology,— namely the very general, but not universal difference in structure between the embryo and the adult;— of parts in the same indivividual embryo, which ultimately become very unlike and serve for diverse purposes, being at this early period of growth alike;— of embryos of different species within the same class, generally, but not universally, resembling each other;— of the structure of the embryo not being closely related to its conditions of existence, except when the embryo becomes at any period of life active and has to provide for itself;— of the embryo apparently having sometimes a higher organisation than the mature animal, into which it is developed? I believe that all these facts can be explained, as follows, on the view of descent with modification.

It is commonly assumed, perhaps from monstrosities often affecting the embryos at a very early period, that slight variations necessarily appear at an equally early period. But we have little evidence on this head— indeed the evidence rather points the other way; for it is notorious that breeders of cattle, horses, and various