SECT. i. OF THE LO WER ANIMALS. 1 1 



nuclei, of nervous matter, technically called ganglia, 

 which are centres of nervous energy, each of which is 

 endowed with its own peculiar properties ; the nervous 

 cords and filaments proceeding from them are merely 

 organs of transmission. The arrangement of these 

 centres of nerve-force is symmetrical, or unsymmetrical, 

 according to the form of the animal. 



In the lower portion of Articulated animals, such as 

 insects, Crustacea, annelids, worms, &c. &c., there is 

 a double cord extending along the ventral side of the 

 animal, united at equal intervals by double nerve-centres, 

 or ganglia. These two cords diverge towards the upper 

 end, surround the gullet, and unite again above that 

 tube to form a distinct bilobed principal nerve-centre 

 or brain. A third form of the nervous system is only a 

 ring round the gullet ; the points in it from whence the 

 nerves radiate are swollen nerve-centres, or ganglia. 

 Those on the sides and upper parts of the ring represent 

 the brain, and supply the eyes, mouth, &c., with nerves : 

 other centres, connected with the lower side of the ring, 

 send nerves to the locomotive organs, viscera, and re- 

 spiratory organs. In animals of a still lower grade there 

 are single nuclei irregularly scattered, but in every case 

 they are centres of energy from whence filaments are 

 sent to the different parts of the creature. The last 

 and lowest system consists of filamentous nerves, chiefly 

 microscopic. 



Intelligence, or the mental principle, in animals differs 

 in degree, though not in kind, from that in the human 

 race. It is higher in proportion as the nervous system, 

 especially the brain, approximates in structure to that of 

 man ; but even in many of the lower orders may be traced 

 the dawn of that intelligence which has made man 

 supreme on earth. Every atom in the human frame, 

 as well as in that of other animals, undergoes a periodi- 

 cal change by continual waste and renovation ; but the 



