In the eyes of most naturalists, the structure of the embryo is even more important for classification than that of the adult. For the embryo is the animal in its less modified state; and in so far it reveals the structure of its progenitor.

Man, like every other animal, has no doubt advanced to his present high condition through a struggle for existence consequent on his multiplication; and if he is to advance still higher, it is to be feared that he must remain subject to a severe struggle.

For no amount of exercise, or habit, or volition, in the utterly sterile members of a community could possibly affect the structure or instincts of the fertile members, which alone leave descendants. I am surprised that no one has advanced this demonstrative case of neuter insects, against the well-known doctrine of Lamarck.

On the ordinary view of each species having been independently created, we gain no scientific explanation.

Embryology will reveal to us the structure, in some degree obscured, of the prototypes of each great class.

The expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient.