62 ARTICULATED ANIMALS. 



masses, or centres of perception. In all creatures, however, be- 

 longing to the articulate division of the animal kingdom, the 

 nervous system is arranged upon a plan which is sufficiently con- 

 spicuous throughout the entire series. A double chain of brains, 

 or ganglia, runs down the central line of the body beneath the 

 alimentary canal ; and it is from the symmetry conspicuous in 

 the arrangement of these that the most unmistakable character 

 whereby the Articulata are distinguished is furnished. 



The first pair of brains or ganglia is always situated in the head, 

 and supplies nerves to the eyes, to the antennae, and to all the 

 principal instruments of sensation; on the proportionate size 

 and development of these ganglia the perfection of the senses 

 possessed by any of these creatures depends, consequently they 

 are generally spoken of as the brain. 



FIG. 57. NERVES OF LEECH AND COCKCHAFER. 



All the other ganglia are arranged in a double series along the 

 floors of the different segments of the body, each supplying the 

 muscles belonging to the rings in its neighbourhood. In propor- 

 tion to the size and perfection of these ganglia, therefore, will be 

 the energy of the creature's movements. In the annexed en- 

 graving (Fig. 57), representing the nervous system of a leech and 

 of a cockchafer, it will be seen that in the former the nervous 

 centres are numerous and feeble, corresponding with the imper- 

 fection of the organs of sense and the absence of limbs, whereas 

 in the latter they are proportionately large and few in number, 

 adapted to the possession of senses of a higher description, and 

 limbs endowed with great strength and activity. 



The Articulata are divided into five principal classes, as repre- 

 sented in the following table : 



