§ 10. ANALOGY NOT IDENTITY. 603 



of some peculiar modification of that mysterious vital force 

 we term nervous influence, are questions to which, I 

 apprehend, no satisfactory reply can be given. 



In fine, a minute globular cell is typical of the common 

 germ from which all organic fabrics proceed. All animals 

 and plants, therefore, may justly be regarded as definite 

 aggregations of cells, endowed with specific properties in 

 the different types, and subjected to a never-varying law of 

 development ; and in animals, as well as in plants, there are 

 certain kinds in which the entire organism consists of but 

 a single cell ;* and others in which each individual is but 

 a cluster of such cells arranged in a definite manner. 

 These mere aggregations of cells perform all the functions 

 of animal life, viz., the maintenance of a particular form for 

 a certain period, the elaboration of materials of support 

 from food, locomotion, and the perpetuation of the species ; 

 hence these animals, like the simplest plants, may be 

 divided without losing their vitality, and every part may 

 become a perfect individual. To this class belongs the 

 Hydra, and the above exposition of its structure renders the 

 production of several animals from the vivisection of an 

 individual, perfectly intelligible. 



10. Analogy not Identity. — And here I must briefly 

 comment on the doctrine of the law of development, as it 

 is termed, so speciously, but unphilosophically, advocated 

 in a recent work ;f in which it is attempted to show, that 

 all the varied forms of organic life are the result of a 

 law, by which is produced an unbroken chain of gradually 

 exalted organization, from the crystal to the globule, and 

 thence through successive stages of the polype, mollusk, 

 &c. up to Man.f 



* The Monads : see " Thoughts on Animalcules," Plate II. 

 f Vestiges of the Natural History of the Creation. 

 t The following remarks of Sir John Herschel on this theory are 

 too important to be omitted. " The transition from an inanimate 



