INSECTA. 205 



verse nerve to the right and to the left, to which I give the name of 

 spinal rein (bride epiniere). Of these transverse nerves there are 

 ten pairs ; they terminate chiefly in the stigmata and tracheae, but 

 send off small branches to the skin and to the dorsal vessel. These 

 are the respiratory ganglia and nerves, and have been erroneously 

 considered as the motor column and nerves. 



The nervous system in perfect insects approaches to its larval con- 

 dition according as the segments of the body and their locomotive 

 appendages are less concentrated and developed ; thus, in the darkling 

 beetle {JMeloe) the abdominal nervous columns still manifest eight 

 distinct ganglions, of which the last, perhaps including three ganglions 

 of the larva, is now the largest, and radiates its branches to the gene- 

 rative organs. The first, or sub-cesophageal ganglion, sends forward 

 four median branches to the under parts of the mouth, and is connected 

 with the brain by the two lateral chords forming the post-oesophageal 

 collar. The usual nerves are given off from the brain, those to the 

 eyes having acquired an increase of bulk, corresponding with the 

 great change in the size and complexity of the organs of vision. The 

 stomato-gastric nerves arise close to the antennal branches, and form 

 a median frontal ganglion, and are connected with a pair of lateral 

 ganglions : from these the usual recurrent nerve is given off. In the 

 thorax w^e distinguish the second ventral ganglion, which, as it dis- 

 tributes branches to the first pair of legs, I have called the brachial 

 ganglion. The third ventral ganglion supplying, amongst other parts, 

 the elytra, may be termed the elytral ganglion. The fourth ventral 

 ganglion is distinct in the present species, and, supplying the nerves to 

 the second or true wings, may be termed the alar ganglion. The fifth, 

 sixth, and seventh, or first three ganglions in the abdomen, distribute 

 nerves to as many large and moveable segments of that division of the 

 trunk : the last ganglion is the largest, and its size is conformable 

 with the bulk of the generative apparatus, upon which, on the rectum, 

 and the modified terminal segments of the abdomen, its branches are 

 expended. 



In insects having the organs of flight better developed, the elytral 

 and alar ganglia present a greater proportional size ; but different 

 degrees of concentration in the centres of the nervous system are 

 met with in these higher forms of insects. In the Blattae, for ex- 

 ample, there are as many as ten distinct ventral, or inferior ganglions. 

 The supra-cesophageal nervous centre or brain is a transversely 

 oblong bilobed mass, sending its upper and largest pair of nerves 

 to the eyes. Anterior and below the antennal nerves arise from small 

 mamillary processes of the brain, reminding us of olfactive lobes. 

 The stomato-gastric nerves are seen a little in advance of those 



