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 sh 
on a larger scale in fig. 188; where a 3B, 
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 6b. These branches are distri- 
buted to the air-tubes and other parts of the — 
Fig.188.—Portionor respiratory apparatus, and communicate 
tau Or Iaecery’ With those of the other system. We shall | 
Showing the respira. find that, even in the highest Vertebrata, 
ratory ganglia and there is a portion of the nervous centres — 
5 jah 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, Inthe 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 — 
‘ 
, 
ee 
\ 
Y -----—-- ES 
Bs 
Vee 
° 
" yi , 
= 
fk 
iN, 
y 
) Vie Z| 
SS 
ca | 
eg eee ge Pee ee 
Fig. 189.—Nervous System or Crap (Maia). 
ea, upper part of the shell laid open; a, antenne; y, eyes; e, stomach; c, cephalic 
ganglion; no, optic nerves; co, cesophageal collar; ms, stomato-gastric nerves; 
#, thoracic ganglionic mass; np, nerves of the legs, na, abdominal nerve. 
