Long ago Professor Broca and Mr. Herbert Spencer pointed to the facts of co-adaptation, or co-ordination within the limits of the same organism, as presenting good evidence of Lamarckian principles, working in association with natural selection. Thus, taking one of Lamarck's own illustrations, Mr. Spencer argued that there must be numberless changes--extending to all the organs, and even to all the tissues, of the animal--which in the course of many generations have conspired to convert an antelope into a giraffe. Now the point is, that throughout the entire history of these changes their utility must always have been dependent on their association. It would be useless that an incipient giraffe should present the peculiar form of the hind-quarters which we now perceive, unless at the same time it presented the correspondingly peculiar form of the fore-quarters; and as each of these great modifications entails innumerable subordinate modifications throughout both halves of the creature concerned, the chances must have been infinitely great against the required association of so many changes happening to have arisen congenitally in the same individuals by way of merely fortuitous variation. Yet, if we exclude the Lamarckian interpretation, which gives an intelligible _cause_ of co-ordination, we are required to suppose that such a happy concurrence of innumerable independent variations must have occurred by mere accident--and this on innumerable different occasions in the bodies of as many successive ancestors of the existing species. For at each successive stage of the improvement natural selection (if working alone) must have needed all, or at any rate most, of the co-ordinated parts to occur in the same individual organisms[37]. [37] For another and better illustration more recently published by Mr. Spencer, see _The Inadequacy of Natural Selection_, p. 22. In alluding to what I have already published upon the difficulty which thus appears to be presented to his theory, Weismann says, "At no distant time I hope to be able to consider this objection, and to show that the apparent support given to the old idea [i. e. of the transmission of functionally-produced modifications] is really insecure, and breaks down as soon as it is critically examined[38]." [38] _Essays on Heredity_, vol. i. p. 389. [For further treatment of the subject under discussion _see_ Weismann, _The All-sufficiency of Natural Selection_ (Contemp. Rev. Sept. and Oct. 1893), and _The Effect of External Influences upon Development_. "Romanes Lecture" 1894, and Spencer, _Weismannism once more_ (Cont. Rev. Oct. 1894). C. Ll. M.]