1864.] DR. DAWSON ON CLASSIFICATION OF ANIMALS. 251 



guish it from mineral substances, but not from the plant, -ivhich is 

 also organised and living, though in a mode somewhat diiferent. 



To distinguish the animal from the plant, we may affirm, 1st, 

 that it is reproductive by eggs and not by seeds ; 2nd, that in its 

 processes of nutrition it digests organic food in an internal cavity, 

 subsequently consuming a part of this food at the expense of the 

 oxygen of the atmosphere; and that it builds up its tissues prin- 

 cipally of nitrogenised matter ; 3rd, that the animal possesses the 

 power of voluntary motion, and, to subserve this, muscular tissue; 

 4th, that it possesses sensation, and, to subserve this and motion 

 as well, a nervous system and external senses. 



"We thus find four general characteristics of the animal : 



1. Sensation — by means of a nervous system and special 



senses. 



2. Voluntary motion — by means of the muscular and nervous 



systems. 



3. Nutrition — by means of a stomach and intestines, with 



absorptive, circulatory, and respiratory apparatus. 



4. Reproduction — by ova and sperm-cells. 



In every animal, even the simplest, these functions are in 

 greater or less perfection performed ; and it is the presence of the 

 aggregate of these functions or the organs proper to them, that 

 enables us to call any organism an animal. It is important to carry 

 with us this definition of the animal ; first, as indicating the limits 

 of the creatures which the zoologist has to classify ; and secondly, 

 as pointing out to us the nature of the characters on which we 

 must rely, in our classification. For the student I hold it to be 

 necessary, before proceeding further, to understand well these 

 functions and structures, as they exist in some one of the higher 

 animals. 



5. Primary Division of Animals into Provinces or 



Branches. 



This, on the principles already stated, must be made solely on 

 the ground of type or plan, and this taken in its most general 

 aspects. 



If we bring before us mentally the several members of the ani- 

 mal kingdom, we shall probably be struck in the first instance 

 with the general prevalence of bilateral symmetry, or the arrange- 

 ment of parts equally on the right and left sides. We may 

 observe, however, that there is a large group of animals to which 



