§ 265. The questions to be treated under the above title are widely different from those which it ordinarily expresses. We have no alternative, however, but to use Physiology in a sense co-extensive with that in which we have used Morphology. We must here consider the facts of function in a manner parallel to that in which we have, in the foregoing Part, considered the facts of structure. As, hitherto, we have concerned ourselves with those most general phenomena of organic form which, holding irrespective of class and order and sub-kingdom, illustrate the processes of integration and differentiation characterizing Evolution at large; so, now, we have to concern ourselves with the evidences of those differentiations and integrations of organic functions which have simultaneously arisen, and which similarly transcend the limits of zoological and botanical divisions. How heterogeneities of action have progressed along with heterogeneities of structure--that is the inquiry before us; and obviously, in pursuing it, all the specialities with which Physiology usually deals can serve us only as materials. Before entering on the study of Morphological Development, it was pointed out that while facts of structure may be empirically generalized apart from facts of function, they cannot be rationally interpreted apart; and throughout the foregoing pages this truth has been made abundantly manifest. Here we are obliged to recognize the interdependence still more distinctly; for the phenomena of function cannot even be conceived without direct and perpetual consciousness of the phenomena of structure. Though the subject-matter of Physiology is as broadly distinguished from the subject-matter of Morphology as motion is from matter; yet, just as the laws of motion cannot be known apart from some matter moved, so there can be no knowledge of function without a knowledge of some structure as performing function.