[42] _Nature_, vol. xliii. pp. 410, 557; vol. xliv. pp. 7, 29. I say "adopted," because I had objected to his quoting the analogy of artificial selection, and stated, as above, that the only way to meet Mr. Spencer's "difficulty" was to deny the fact of co-adaptation as ever occurring in any case. It then appeared that Professor Meldola agreed with me as to this. But I do not yet understand why, if such were his view, he began by endorsing Mr. Wallace's analogy from artificial selection--i. e. confusing the case of co-adaptation with that of the blending of adaptations. If any one denies the fact of co-adaptation, he cannot assist his denial by arguing the totally different fact that adaptations may be blended by free intercrossing; for this latter fact has never been questioned, and has nothing to do with the one which he engaged in disputing. Now, if we are agreed that the only question in debate is the question of fact whether or not co-adaptation ever occurs in nature, it appears to me that the best field for debating the question is furnished by the phenomena of reflex action. I can well perceive that the instances adduced by Broca and Spencer in support of their common argument--such as the giraffe, the elk, &c.--are equivocal. But I think that many instances which may be adduced of reflex action are much more to the point. _For it belongs to the very nature of reflex action that it cannot work unless all parts of the machinery concerned are already present, and already co-ordinated, in the same organism._ It would be useless, in so far as such action is concerned if the afferent and efferent nerves, the nerve-centre, and the muscles organically grouped together, were not all present from the very first in the same individuals, and from the very first were not co-ordinated as a definite piece of organic machinery.