VII THE STUDY OF ZOOLOGY 207 



is a species, our cray fish is another, our prawn is 

 another. In other countries, however, there are 

 lobsters, cray fish, and prawns, very like ours, and 

 yet presenting sufficient differences to deserve dis- 

 tinction. Naturalists, therefore, express this re- 

 semblance and this diversity by grouping them as 

 distinct species of the same "genus." But the 

 lobster and the cray fish, though belonging to dis- 

 tinct genera, have many features in common, and 

 hence are grouped together in an assemblage which 

 is called a family. More distant resemblances 

 connect the lobster with the prawn and the crab, 

 which are expressed by putting all these into the 

 same order. Again, more remote, but still very 

 definite, resemblances unite, the lobster with the* 

 woodlouse, the king crab, the water flea, and the 

 barnacle, and separate them from all other animals ; 

 whence they collectively constitute the larger 

 group, or class, Crustacea. But the Crustacea 

 exhibit many peculiar features in common with 

 insects, spiders, and centipedes, so that these are 

 grouped into the still larger assemblage or " pro- 

 vince" Articulata; and, finally, the relations 

 which these have to worms and other lower 

 animals, are expressed by combining the whole vast 

 aggregate into the sub-kingdom of Annulosa. 



If I had worked my way from a sponge instead 

 of a lobster, I should have found it associated, by 

 like ties, with a great number of other animals 

 into the sub-kingdom Protozoa ; if I had selected 

 a fresh-water polype or a coral, the members of 



