PREFACE. ALTHOUGH the observations recorded in the following pages have necessarily led the author to give expression to a general view or doctrine which seems to him to account for the appearances observed, he thinks it right to state that the conclusions which have now assumed a definite form have gradually grown upon him during the course of observations extending over a period of several years. In fact some of the drawings in this volume, and others which have been published elsewhere, equally favorable to the view, were made long before any specific theory had been arrived at. An attempt has been made to account for the anatomical characters of certain tissues and to trace the changes which take place during the development, growth, nutrition, and decay of individual textures. The results obtained, it need scarcely be said, are very |