ARTICULATA. 213 



CHAPTER XIV. 



ARTICULATA. 



" Yet wert thou once a worm a thing that crept 

 On the bare earth, then wrought a tomb, and slept ! 

 And such is man ; soon from his cell of clay 

 To burst a seraph in the blaze of day ! " ROGERS. 



I. THE Articulated type of animals (Lat., articulus, a 

 joint) includes all which possess a distinctly jointed 

 body, as Worms, Crustacea, and Insects. It contains a 

 greater number and variety of forms than all the other 

 types put together. The nervous system consists chiefly 

 of a double chain of ganglia along the ventral surface of 

 the abdomen, connected together by nerve-filaments. 

 The part representing the brain is in the form of a ring 

 encircling the gullet. The circulatory apparatus is a 

 tubular structure running along the back, and communi- 

 cating with the body-cavity. The limbs, when present, 

 are jointed and hollow, and on the same side as the 

 nerve-cords. 



There are five classes of Articulates : the aquatic 

 Worms and Crustaceans, and the air-breathing Spiders, 

 Myriapods, and Insects. It must be remembered, in 

 accordance with the principles so often referred to in the 

 present work, that the order of classes in a type is one 

 of relation rather than of structural rank. Classes can- 

 not be arranged serially, any more than species, as if one 

 was an improvement on another, by progressive devel- 



