20 INTRODUCTION. 



and plants, may be collectively represented, in reference to 

 their mutual relationship, by two cones, one of which is in- 

 verted on the other, so that their summits are brought into 

 mutual contact. For there is a point of departure common 

 to both of these grand divisions of living nature, THE 

 ORGANIC CELL, which animated, commences the animal 

 series, and remaining immovable, serves as the basis of the 

 vegetable creation. This organic cell may be imagined to 

 be situated at the apex of the cones, the lower cone repre- 

 senting the vegetable and the upper one the animal creation. 

 Plants and animals increase in organic simplicity and the 

 analogies between them multiply and become more striking 

 in proportion to their approach to this point ; while, on the 

 contrary, the differences which separate them increase and 

 their organization becomes more complicated, as they elon- 

 gate from it. 



All that variety of form which marks the external 

 organs both of plants and animals, is clearly traceable to 

 the same organic laws. Thus, the same organ which attains 

 a high degree of development in one plant or animal, is for 

 certain physiological reasons in another, either suppressed 

 altogether or reduced to a rudimentary condition. But 

 these changes take place almost imperceptibly. We never 

 see an important organ disappear all at once in any of the 

 classes of the animal and vegetable kingdom. It is by de- 

 grees that the organ loses in succession the several parts 

 which complicated it ; these become rudimentary, and the 

 organ is finally reduced to the utmost degree of structural 

 simplicity, those parts alone remaining which are absolutely 

 essential to enable it to perform its function. What are 

 called varieties by naturalists are, in fact, only different 

 phases in the organic development of the same specific 

 form j and a truly scientific classification can only be 



