I have always put it to myself--What advantage can we see in an infusory animal, or an intestinal worm, or coral polypus, or earthworm being highly developed?
If no advantage, they would not become highly developed: not but what all these animals have very complex structures (except infusoria), and they may well be higher than the animals which occupied similar places in the economy of nature before the Silurian epoch.

There is a blind snake with the appearances and, in some respects, habits of earthworms; but this blind snake does not tend, as far as we can see, to replace and drive out worms.

I think I must in a future edition discuss a few more such points, and will introduce this and H.C.

Watson's objection about the infinite number of species and the general rise in organisation.

But there is a directly opposite objection to yours which is very difficult to answer--viz.