AUTHOR'S PREFACE. 



It is one of the essential advantages of the present age, 

 that the bond of nnion 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 there- 

 fore renders it so much the more remarkable, that, notwith- 

 standing 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 conclu- 

 sions 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 develop- 

 ment of the elementary parts of animals and plants. 



The principal result of this investigation is, that one com- 

 mon principle of development forms the basis for every sepa- 

 rate 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 im- 

 portance in an historical point of view in reference to the 

 development of this idea. 



