24 THOUGHTS ON ANIMALCULES. 



varying in size from infinite minuteness to forms visible 

 to the unassisted eye. In fine, a minute globular cell 

 is typical of the common germ from which all organic 

 fabrics proceed. All animals and plants 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 



* Although it is now a received physiological axiom, that cells are the 

 elementary basis, the ultimate limit, of all animal and vegetable structures, 

 and that the varied functions in which organic life essentially consists are 

 performed by the agency of cells, which are not distinguishable from each 

 other by any well marked characters, there is not the slightest ground for 

 assuming any identity between the primary cells even of the simplest 

 species of animals or vegetables, much less between those of more com- 

 plicated organisation. The single cell, which embodies vitality in the 

 yeast fungus or in the monad, is governed by the same immutable or- 

 ganic laws which preside over the complicated machinery of Man and the 

 other vertebrata ; and the single cell, which is the embryotic condition of 

 the Mammal, has no more relation to the single cell, which is the per- 

 manent condition of the Monad, than has the perfect animal into which 

 the mammalian cell ultimately becomes developed. The cell that forms 

 the germ of each species of organism is endowed with special properties, 

 which can result in nothing but the fabrication of that particular species. 

 The serious error which pervades the theory advanced in the work inti- 

 tled " The Vestiges of the Natural History of the Creation" has arisen 

 from its author having, in many instances, assumed analogy to be a proof 

 of identity. There is an analogy between the human embryo and the 

 monad of the Volvox, in that each consists of simple cells ; but there is no 

 more identity between the human and the polygastrian cells, than be- 

 tween the perfect man and the mature animalcule. 



