12 COJIPARISONS OF STRUCTURE IN ANIMALS. 



and others; to the barnacles, all arranged in 

 their respective classes. 



The next sub-kingdom, containing the cnis- 

 taceous animals, as crabs and lobsters ; the 

 spiders and scorpions ; true insects ; the myria- 

 pods, millipedes, etc. ; and the ringed worms, 

 as the earthworm, leech, etc. In this sub- 

 kingdom there are nerves uniting together a 

 series of nervous knots termed ganglia, distri- 

 buted with systematic regularity. The body 

 consists of a succession of rings or annulations, 

 formed by the integument, which may be soft, 

 as in the leech, or rigid and calcareous, as in 

 the lobster. 



The next sub-kingdom comprehends the 

 sea-urchins and star-fishes ; the tripangs, so 

 much esteemed in China as delicacies of the 

 table ; certain parasitic worms, as the guinea- 

 worm, and the various species of ascaris; the 

 wheel animalcules, and a group of curious 

 zoophites, called moss corals, of which the 

 flustra, common along our coasts, is an ex- 

 ample. In this sub -kingdom the nerves, where 

 traceable, appear in the form of minute 

 threads diversely arranged. 



The last sub-kingdom enjbraces the sea- 

 anemones, the ordinary zoophites and coral- 



