CONCENTRATION OF GANGLIA IN HIGHEST INVERTEBRATA. 361 
greater extent that which has been already noticed in the per¬ 
fect Insect (§ 441). Thus in the Spider , the cephalo-thorax 
contains a single large ganglion (t, fig. 46), from which all the 
legs are supplied. The same is the case in the Crab , whose 
nervous system is represented in fig. 189. Besides this mass, 
t, however, which is situated beneath the alimentary canal, 
there is a single or double cephalic ganglion, c, which receives 
the nerves from the organs of sense, and sends backwards, to 
communicate with the mass t , a pair of cords that separate to 
give passage to the oesophagus, round which they form a sort 
of collar co. And there are other small ganglia and nerves, 
connected with the operations of mastication and digestion, 
which are called stomato-gastric (from two Greek words, 
meaning the mouth and the stomach). 
448. A similar concentration, though with a different 
arrangement of parts, is seen in the nervous system of the 
Poulp, one of the Cephalopoda (§ 111). There is still a 
nervous collar through which the oesophagus passes (a, fig. 
190); but the organs of locomotion being the enlarged tenta- 
cula that surround the mouth, the nerves given off to them 
arise from ganglia that form part of the cephalic mass, b , b, 
instead of being located at a distance from it. At o are seen 
the optic nerves, proceeding from distinct ganglia; and at c 
is a heart-shaped ganglionic mass, which seems to bear more 
resemblance to the proper brain of higher animals, than does 
any that we elsewhere find in the Invertebrata. In front of 
this are two ganglia on the middle line, both of which belong 
to the stomato-gastric system, one supplying the lips and the 
other the pharynx. From the mass g , situated beneath the 
oesophagus, there pass backwards two cords m m, each of 
which has a ganglion e upon its course, and from this are 
given off nerves to the general surface of the mantle; and also 
other two cords, which run backwards to supply the viscera, 
and especially the gills,—each passing through a long narrow 
ganglion r, before entering them. It would seem as if the 
ganglia e and r corresponded with the ganglia c and b in the 
Aplysia; but as if, in consequence of the great enlargement 
of the cephalic mass, they were proportionally reduced in 
size. 
449. In the nervous system of Vertebrated animals, the 
ganglia are no longer scattered through the body, but are 
