CLASSIFICATION IN THE ANIMAL KINGDOM. 23 



The third is hardly correct, since the lowest animals have no apparent 

 nervous or muscular system, and, in their case, we cannot be sure of 

 voluntary motion. Spontaneous movements are seen in many plants. 

 The fourth is a mere assumption, not aifording the least assistance as 

 a means of distinction. Sensation cannot he proved in the lowest 

 animals, nor its total absence in plants; and there are animals without 

 organs of sense, or any distinct nervous system. Even in the second 

 distinction, it is hardly safe to refer to the animal building up its 

 tissues chiefly of nitrogenized matter, since some known animal tissues 

 are of the same nature as cellulose, and nitrogen is found in the 

 protoplasm in every active vegetable cell. The best distinctions seem 

 to be, that in the animal the means of absorbing nutriment are within 

 the animal frame, the food being brought within the body before it is 

 placed within reach of the absorbents, whilst in the plant the absorb- 

 ents are external ; and that the animal is nourished by organized 

 substances, animal or vegetable, fresh, or more or less decaying, whilst 

 the vegetable lives upon water, gaseous substances,'.and salts or metals, 

 in a condition to be dissolved in water, but never directly upon organ- 

 ized matter. Dr. Dawson has here expressed widely prevalent views, 

 presented, in some form, in most introductions to zoology and botany ; 

 and, though hardly necessary to my object in this paper, I have 

 taken the opportunity of giving my reasons for rejecting some of the 

 tests commonly recommended for distinguishing the kingdoms. The 

 remainder of the section, in establishing the four general characteristics 

 of the animal, attempts to lay the foundation of that quaternary system 

 in zoological classification which the learned and ingenious author is 

 ■disposed to favour. As sensation, motion, nutrition and reproduc- 

 tion are the four great functions of animal life, it is concluded, not 

 without great plausibility, that the predominance of each of these in 

 turn will constitute a great division of the animal kingdom, whilst 

 under each of these again a similar cause will produce four secondary 

 modifications, and so on through all the variations which occur. I 

 am myself well persuaded that the beautiful harmony of plan, whicb 

 <;laims the perpetually renewed admiration of the intelligent obser- 

 ver of nature, is due to certain tendencies of development in respect 

 to the great functions of life, which, after being manifested in the 

 great branches or sub-kingdoms, are repeated under each secondary 

 type, so as to cause the number of groups at each step in subdivision 

 !to be, so far as they exist and are known to us, the same, but whilst 



