CLASSIFICATION AND CREATION. 67 



with each other, remain the same. The respi- 

 ratory organs, which in most of the Worms were 

 mere vesicles on the lower part of the sides of 

 the body, are here more highly organized gills ; 

 but their general character and relation to other 

 parts of the structure are unchanged, and there 

 is a connection between the gills and the legs 

 in Crustacea, corresponding to that between the 

 respiratory organs in Worms and their locomo- 

 tive appendages. The alimentary canal consists 

 of a single digestive cavity passing through the 

 whole body, as in Worms, the anterior part of 

 which is surrounded by a large liver. What is 

 true of the Lobsters is true also, so far as class- 

 characters are concerned, of all the Crustacea. 



Highest in this type are the Insects, and among 

 these I include Spiders and Centipedes as well as 

 Winged Insects. It is true that the Centipedes 

 have a long uniform body like Worms, and the 

 Spiders have the body divided into two regions 

 like the Crustacea, while the body in true Insects 

 lias three distinct regions, head, chest, and hind- 

 body ; but, notwithstanding this apparent differ- 

 ence, both the former share in the peculiar 

 class-character that places them with the Winged 

 Insects in one class, distinct from all the other Ar- 

 ticulates. We have seen that in the Worms the 

 respiratory organs are mere vesicles, while in the 

 Crustacea they are more highly organized gills ; 



