INTRODUCTION. 15 



under envelopes more or less resisting, encloses a germ. 

 In this germ, all the organs of the adult animal and plant 

 exist in a rudimentary undeveloped condition. Germina- 

 tion, or the act by which these organs disengage themselves 

 from their envelopes, does not increase their number, but 

 only augments their size or modifies their form. The seed 

 contains the plant, and the egg the animal. Thus, they 

 are alike at the commencement of their being. In the 

 second place, the organs of plants and animals,— the root, 

 stem, and leaves of the former, the bones, muscles, and 

 limbs of the latter, — will not grow without a plentiful sup- 

 ply of food and air. In both instances it is absolutely 

 necessary that the nutritive aliment should be introduced 

 into the interior of the plant or the animal, and be dis- 

 tributed to all the parts of their organization. Now the 

 absorption, circulation, and assimilation of food and air, by 

 animals and plants, is in principle precisely the same 

 process. Abundant proof of this position will be given 

 in the succeeding pages. 



Well-marked and obvious distinctions between animals 

 and plants exist only in the more highly organized forms 

 of animal and vegetable life. As we descend to beings of 

 a lower rank in creation, these distinctions become gra- 

 dually effaced, and we see successively disappear the most 

 important organs of animal life. The organs of the senses 

 become rudimentary, bones, blood vessels, and nerves to- 

 tally disappear, and in proportion as the powers of animal 

 life are suppressed, those which are truly vegetative gain' 

 the ascendancy. Thus, the lower orders of the cold- 

 blooded vertebrata, whose bodily temperature is regulated 

 by that of the medium in which they live, become torpid 

 and inactive in common with plants in winter. So also 

 many vertebrated and crustaceous animals change their 



