NERVOUS SYSTEM OF ARTICULATA. 



77 



equal, and form with their connecting filaments two chains re- 

 sembling knotted cords, extending from one end of the body to the 

 other. (Fig. 290.) But in proportion as we rise in the scale, we 

 see the ganglia approach one another, both sideways and length- 



FIGS. 290 and 201. Anatomy of the Caterpillar and Moth of the Privet : a, cephalic 

 ganglia, situated in front of the oesophagus, and giving origin to the nerves of the 

 eyes, &c. ; b, cords which unite these ganglia to those of the second pair, passing on 

 either side of the oesophagus, so as to form a collar round it ; c, first pair of sub-ceo- 

 phageal ganglia ; d, ganglion of the first segment of the thorax, followed in the Cater- 

 pillar by others at regular intervals ; e, nervous mass in the Moth, formed by the ganglia 

 of the second and third thoracic segments ; /, abdominal ganglia; h, mouth ; i, trunk ; 

 j, oesophagus ; k, stomach ; I, intestine and biliary vessels ; m, large intestine ; n, anus ; 

 o, legs of the first pair ; p, legs of the second pair ; q, legs of the third pair ; r, first pair 

 of membranous legs, in the Caterpillar ; *, dorsal vessel ; t, first segment of the thorax ; 

 , horny appendage at the extremity of the abdomen of the Caterpillar. 



wise ; so that each pair unites on the central line into a single mass ; 

 whilst the ganglia of different segments are also brought together 

 into one spot, and so combined as to form but one large ganglion, 

 as we shall hereafter notice especially among the Crustacea. 

 This centralization is sometimes carried so far, in certain Crabs 

 for example, that there exist in the whole body but two nervous 

 masses, one in the head, and the other in the thorax (Fig. 466). 

 The ganglia which we find in the head of Articulata have a 



