Secondly, I was greatly interested by the abstract in 'Nature' of your work on Echinoderms; the complexity, with simplicity, and with such curious co-ordination of the nervous system, is marvellous; and you showed me before what splendid gymnastic feats they can perform. Thirdly, Dr. Roux has sent me a book just published by him, 'Der Kampf der Theile,' &c., 1881 (240 pages in length). He is manifestly a well-read physiologist and pathologist, and from his position a good anatomist. It is full of reasoning, and this in German is very difficult to me, so that I have only skimmed through each page, here and there reading with a little more care. As far as I can _imperfectly_ judge, it is the most important book on evolution which has appeared for some time. I believe that G. H. Lewes hinted at the same fundamental idea, viz. that there is a struggle going on _within_ every organism between the organic molecules, the cells, and the organs. I _think_ that his basis is that every cell which best performs its function is as a consequence at the same time best nourished and best propagates its kind. The book does not touch on mental phenomena, but there is much discussion on rudimentary or atrophied parts, to which subject you formerly attended. Now if you would like to read this book, I will send it after Frank has glanced at it, for I do not think he will have time to read it with care. If you read it and are struck with it (but I may be _wholly_ mistaken about its value), you would do a public service by analysing and criticising it in 'Nature.' Dr. Roux makes, I think, a gigantic oversight in never considering plants; these would simplify the problem for him.