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 Vertebrata, 
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.188.— Portion of 
the Nervous Sys¬ 
tem of Insect; 
Showing the respira- 
ratory ganglia and 
nerves. 
c na 
Fig. 189.— Nervous System of Crab ( Maia ). 
ea, upper part of the shell laid open ; a, antennae ; y, eyes ; e, stomach ; c, cephalic 
ganglion; no, optic nerves; co, oesophageal collar ; ns, stomato-gastric nerves; 
t, thoracic ganglionic mass ; np , nerves of the legs, na, abdominal nerve. 
