168 MANUAL OF NATURAL HISTORY. 



ANNULOSE ANIMALS. 



The classes of the Annulose division of the Ani- 

 mal Kingdom, which is characterised chiefly by the 

 segmented nature of the skin, the possession of 

 jointed limbs, and a double knotted chord of nerv- 

 ous matter, vary greatly among themselves accord- 

 ing to the modifications of their organs of locomo- 

 tion, their breathing system, and their generative 

 apparatus. Thus we find the Cirrhopods, covered 

 with a testaceous envelope, fixed to one spot, and 

 with their legs metamorphosed into breathing or- 

 gans, living in the water ; the Crustaceans, also 

 aquatic animals, respiring by means of gills, and pro- 

 tected by a hard skin composed of carbonate of 

 lime, and having never less than ten legs, but often 

 furnished with many more variously modified ; the 

 Insects, the most highly organized and intelligent 

 of all the Annulose classes, breathing the free air, 

 having only six legs, usually provided with wings, 

 and undergoing a regular metamorphosis ; the 

 Arachnidans, which have eight legs, respire free 

 air, have no wings, and whose head, deprived of 

 antennse, is consolidated with the thorax forming 

 a single piece ; the Aiolopods, comprehending a 

 a large portion of the Ametabolous Insects of Leach 

 and Macleay, in which the number of legs is vari- 

 able, where the head is provided with antennae, and 

 where the metamorphosis is irregular ; and finally 

 the worm-like Annelids, which gradually conduct 



