From what little I know, I cannot help thinking that you underrate the effects of the physical conditions of life on these low organisms.

But I fully admit that I can give no sort of answer to your objections; yet I must add that it would be marvellous if any man ever could, assuming for the moment that my theory is true.
You beg the question, I think, in saying that Protococcus would be doomed to eternal similarity.

Nor can you know that the first germ resembled a Protococcus or any other now living form.
Page 12 of your letter: There is nothing in my theory necessitating in each case progression of organisation, though Natural Selection tends in this line, and has generally thus acted.

An animal, if it become fitted by selection to live the life, for instance, of a parasite, will generally become degraded.

I have much regretted that I did not make this part of the subject clearer.