CONCENTRATION OF GANGLIA IN HIGHEST INVERTEBEATA. 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 oif 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 



