a 



GENERAL REMARKS. 



JL HE animals which come under our observa- 

 tion, in the present essay, belong to the type of 

 Annulosd) and are cbaracterized as having no 

 skeleton; their muscles are attached to the skin, 

 which is hard, or to processes issuing from it ; 

 and the nervous system consists of a series of 

 knots or ganglia, brought into communication 

 by two longitudinal nervous cords. The classes 

 to which these animals belong may be dis- 

 tinguished by the following characters : 



* Gills for respiration. classes. 

 Legs sixteen: antenn*, two 1 j CRUSTACEA> 



or four . . . J 



** Sacs for respiration. 

 Legs twelve: antennae, none... 3. ARACHNOIDA. 



* * * Trachea for resp iration. 



a. No antennce. 



Legs six or eight . . . . 4. ACARI. 



b. Two antenncB. 



Six thoracic legs : abdomen 7 2 MlRIAPODA . 



also, bearing legs 3 



Six thoracic, and no abdo- \ . T _ 



11 / O. 1NSECTA. 



minal legs J 



