AUTHOR'S PREFACE.
IT is one of the essential advantages of the present age, that the bond of union connecting the different branches of natural science is daily becoming more intimate, and it is to the contributions which they reciprocally afford each other that we are indebted for a great portion of the progress which the physical sciences have lately made. This circumstance therefore renders it so much the more remarkable, that, notwithstanding the many efforts of distinguished men, the anatomy and physiology of animals and plants should remain almost isolated, though advancing side by side, and that the conclusions deducible from the one department should admit only of a remote and extremely cautious application to the other. Of late, the two sciences have for the first time begun to be more and more intimately allied. The object of the present treatise is to prove the most intimate connexion of the two kingdoms of organic nature, from the similarity in the laws of development of the elementary parts of animals and plants.
The principal result of this investigation is, that one common principle of development forms the basis for every separate elementary particle of all organised bodies, just as all crystals, notwithstanding the diversity of their figures, are formed according to similar laws. I have endeavoured to explain the design of such a comparison more fully in the commencement of the third section of this treatise, and will now lay before the reader those data which are of most importance in an historical point of view in reference to the development of this idea.
