CLASSIFICATION OF INSECTS. 169 



624. Vertebrated animals (vertebrata). In this 

 division, which is that of man, and of the animals 

 most resembling him, the brain and principal 

 trunk of the nervous system are enclosed in a 

 bony envelope formed by the cranium and ver- 

 tebrae ; to the sides of this intermedial column 

 are attached the ribs and bones of the limbs, which 

 form the frame-work of the body ; the muscles 

 generally cover the bones, whose motion they 

 occasion : this is a single group. 



625. Molluscous animals (molluscata). In this 

 division there is no skeleton ; the muscles are 

 merely attached to the skin, which constitutes a 

 soft contractile envelope, in which, in many species, 

 are formed stony plates, called shells. The ner- 

 vous system is contained within this general 

 envelope, and is composed of several scattered 

 masses connected by nervous filaments : this is a 

 double group. 



626. Annulated animals (annulata). In this 

 division the nervous system consists of long cords, 

 running longitudinally throughout the body, and 

 dilated at intervals into knots or ganglions. The 

 covering or envelope of the body is divided by 

 transverse folds into a certain number of rings, 

 whose teguments are sometimes hard, sometimes 

 soft ; the muscles are situated intervally : this is a 

 double group. 



627. Radiated animals (radiata). The organs 

 of sensation and motion, in the preceding divisions, 



