Zoological Classification. .443. 



If we separate the Vertebrates on the one hand, and the Radi- 

 ates on the other, there remain the Mollusks and Articulates, 

 groups as markedly distinct from each other, as from the other 

 provinces. We may thus obtain by a somewhat different process 

 from that usually employed, the fourfold Cuvierian classification 

 into sub-kingdoms, and this without leaving any distinct place for 

 the Protozoa as a group of this rank. 



Let us next inquire if the Protozoa may rank as a class. Agassiz 

 has well shown that our classes, orders, &c., in zoology are not 

 arbitrary or accidental, but based on the relations of our own 

 minds to the actual order of nature. Classes, he maintains, are 

 formed on the manner in which the plan or type embodied in the 

 province is carried out, so far as ways and means are concerned ; 

 and we may add, of course, with a reference to uses or objects. It 

 seems to have occurred to him that this implies a certain and de* 

 finite number of classes to each province, for he has but three in 

 each of his invertebrate provinces; though he subdivides more 

 minutely in the vertebrates, deviating in this, as it appears to us, 

 from the large general view which he has himself expressed. 



In the Vertebrates four classes have commended themselves to 

 the comnaon sense of mankind, — the mammals, birds, reptiles, and 

 fishes ; and while it is easy, for example, to subdivide the reptiles 

 into two groups, or the fishes into several, these have obviously 

 respectively a less value than the mammals and birds, and conse- 

 quently cannot be classes. What, then, are the ways^ means^ and 

 ends involved in the vertebrate sub-classes ? They are as follows: 

 1st. The mammal 'implies reproduction without metamorphosis, 

 and the highest development of the sensorium and of intelligence. 

 2ndly. The bird implies the highest development of the locomo- 

 tive apparatus, and parts subsidiary to this. 3rdly. The reptiles 

 imply development of the merely vegetative hfe. 4thly. Fishes 

 embody the lowest condition of the external members and respi* 

 ratory process, and of the nervous system. 



A little thought may satisfy us that we cannot suppose a fifth 

 class co-ordinate with these four, however much we may subdivide 

 any one of them. The question remains, do the other provinces 

 admit of more divisions, or of fewer ? K truly co-ordinate with 

 the first, they should admit of the same number, because each 

 type is placed in the same circumstances, in respect to ways, 

 means, and ends. 



