84 STUDIES IN ANIMAL LIFE. 



limbs ; in both it has similar functions. And while 

 the articulata thus approach in structure the verte- 

 brate type, the mollusca are not only removed from 

 that type by many diversities, but a number of them 

 have such affinities with the Eadiate type that it is 

 only in quite recent days that the whole class of 

 Polyzoa (or Bryozoa, as they are also called) has 

 been removed from the Eadiata, and ranged under 

 the Mollusca. 



To quit this topic, and recur once more to the 

 five divisions, we have only the broad outlines of 

 the picture in Yertebrata, Mollusca, Articulata, Ea- 

 diata, and Protozoa ; but this is a good beginning, 

 and we can now proceed to the further subdivisions. 

 Each of these five sub-kingdoms is divided into 

 classes; these, again, into orders; these into fami- 

 lies; these into genera; these into species; and 

 these, finally, into varieties. Thus, suppose a dwarf 

 terrier is presented to us with a request that we 

 should indicate its various titles in the scheme of 

 classification : we begin by calling it a vertebrate ; 

 we proceed to assign its class as the mammalian ; 

 its order is obviously that of the carnivora ; its 

 family is that of the fox, wolf, jackal, etc., named 

 Canidce ; its genus is, of course, that of Canis ; its 

 species, terrier; its variety, dwarf terrier. Inas- 

 much as all these denominations are the expres- 

 sions of scientific research, and not at all arbitrary 

 or fanciful, they imply an immense amount of labor 

 and sagacity in their establishment ; and when we 



