CLASSIFICATION AND CREATION. 67 
with cach 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 
has 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: 
