58 



INTRODUCTION TO ZOOLOGY. 



double "ganglions," as these nervous masses are termed, 

 fi-om which are given off the nerves that proceed to the 

 extremities. From the symmetrical disposition of these 

 nervous centres, Mr. Owen has given to this sub-kingdom the 

 name Homogangliata.* The body in general presents a cor- 

 responding symmetrical form, and consists of a repetition of 

 rings or segments, as in the Earth-worm, or the ^liUepede 

 (Julus, Fig. 37). 



Fig. 37.— Julus, 



The articulated animals are arranged in the following 



classes : — 



Annelldta, Leeches, Earth-worms, &c. 

 Cirripeda, Barnacles and Acom-sheUs. 

 Ciiistacea, Crabs, Lobsters, &c. 

 Insecta, Beetles, Bees, Buttei-flies, &c. 

 Arachmda, Spiders, Scorpions, and Mites. 



* From two Greek words, one signifj-ing " similar," the other " a 

 ganglion," or knot, being the mass of nervous matter from which the 

 nerves diverge. 



