360 



RESPIRATORY NERVES OF ARTICULATA. 



ganglia and their nerves are best seen in the front of the body, 

 where the cords that pass between the ganglia diverge or 

 separate from each other. This is shown 

 on a larger scale in fig. 188; where AB, 

 A B, are two pairs of ganglia in the thoracic 

 region, connected by two cords which di- 

 verge from one another; and between these 

 are seen the small respiratory ganglion a, and 

 its branches b b. These branches are distri- 

 buted to the air-tubes and other parts of the 

 respiratory apparatus, and communicate 

 with those of the other system. "We shall 

 find that, even in the highest Vertebra ta, 

 there is a portion of the nervous centres 

 which is set apart for the maintenance of the 

 respiratory actions, and which may be regarded as the respi- 

 ratory ganglion ; though it is so closely connected with other 

 parts of the mass as to seem but a part of it ( 450). 



447. In the higher Invertebrata, among both the Articulated 

 and the Molluscous classes, we find a tendency to the concen- 

 tration of the ganglia into one or two masses, carrying to a 



Fig.lSS. PORTION OF 

 THE NERVOUS SYS- 

 TEM OF INSECT; 



Showing the respira- 

 ratory ganglia and 

 nerves. 



Fig. 189. NERVOUS SYSTEM OF CRAB (Maia). 



ca, upper part of the shell laid open ; a, antennae ; y, eyes ; e, stomach ; c, cephalic 

 ganglion; no, optic nerves; co, cesophageal collar; ns, stomato-gastric nerves; 

 t, thoracic ganglionic mass ; np, nerves of the legs , na, abdominal nerve. 



