488 OP THE NERVOUS SYSTEM AND ITS ACTIONS. 



repeated in like manner, in accordance with the condition of the 

 respiratory apparatus ; this being diffused through the whole body, in 

 most of the Articulata, instead of being restricted to one spot as in the 

 Mollusca. The system of respiratory nerves consists of a chain of 

 minute ganglia, lying upon the larger cord, and sending off its delicate 

 nerves between those that proceed from the ganglia of the latter, as 

 seen in Fig. 2. These respiratory ganglia and their nerves are best 

 seen in the thoracic portion of the cord, where the cords of communica- 

 tion between the pedal ganglia diverge or separate from one another. 

 And this is particularly the case in the Pupa state, when the whole 

 cord is being shortened, and their divergence is increased. The tho- 

 racic portion of the cord, in the Pupa of the Sphinx ligustri, is shown 

 in Plate II. , Fig. 4 ; where , , and c, represent the 2d, 3d, and 4th 

 double ganglia of the ventral cord ; d, d, the cords of connexion 

 between them, here widely diverging laterally; and e, e, the small 

 respiratory ganglia, which are connected with each other by delicate 

 filaments that pass over the ganglia of the ventral cord, and which send 

 off lateral branches, that are distributed to the air-tubes and other parts 

 of the respiratory apparatus, and communicate with those of the other 

 system. 



863. Besides the respiratory system of ganglia and nerves, there is 

 in Insects, as in some Molluscs, a set of minute ganglia, which is espe- 

 cially connected with the acts of mastication and swallowing, its fila- 

 ments being distributed to the muscles of the mouth and pharynx, and 

 some of its ganglia being even found on the stomach, where that organ 

 is remarkable for its muscular powers. The number and arrangement 

 of these ganglia vary considerably in different animals, even in those 

 of the same group : but some traces of this distinct system, which is 

 designated as the stomato-gastric, may always be found. One of the 

 minute ganglia appertaining to it, and forming its anterior termination, 

 is seen to lie on the median line, in front of the great cephalic ganglia, 

 in Plate II. , Fig. 3, c. From this a trunk passes backwards along the 

 oesophagus ; which may be likened to the oesophageal branches of the 

 Par vagum in Vertebrata. Two other small ganglia communicating 

 with this, are seen at c?, d. 



864. We are not without traces, moreover, among Invertebrated 

 animals, of the Sympathetic system of the higher classes ; though it is 

 quite a mistake to compare the entire system of nerves and ganglia in 

 the former, with the Sympathetic system of the latter, as was formerly 

 done. The chief distribution of the branches of the Sympathetic of 

 Vertebrata is upon the walls of the blood-vessels, and upon the muscular 

 substance of the heart and alimentary canal ; and it is by the passage 

 of some of the filaments, from the system of minute ganglia just 

 pointed out, to the dorsal vessel, that we recognise it as combining the 

 functions of the Sympathetic with those of the gastric and cardiac por- 

 tions of the Par vagum. It will be remembered that there is a frequent 

 inosculation between these two nerves, even in the highest animals. 



865. Thus we have seen that, in Invertebrated animals, the Nervous 

 System consists of a series of isolated ganglia, connected together by 

 fibrous trunks. The number of these ganglia, and the variety of their 



