362 LECTURE XVI. 



with the super-oesophageal ganglion 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, cor- 

 responding with the great change in the size and complexity of the 

 organs of vision. The stomato-gastric nerves arise close to the an- 

 tennal branches, and form a median frontal ganglion, and are con- 

 nected with a pair of lateral ganglions : from these the usual recurrent 

 nerve is given off. In the thorax we distinguish the second ventral 

 ganglion, which, as it distributes 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 example, 

 there are as many as ten distinct ventral or inferior ganglions. The 

 super-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 in the deflected 

 part of the head. The oesophageal chords are short, uniting in a maxil- 

 lary ganglion, or first of the ventral series, which is situated in the 

 head ; the inter-communicating chords, which pass from this to the 

 brachial ganglion, are long, straight, parallel, and juxta-posed. The 

 brachial ganglion sends off two large and two small pairs of nerves ; 

 the anterior ones are distributed to the muscles of the arm, which are 

 lodged within the anterior portion of the thoracic shield ; the second 

 nerve is continued to the terminal segment of the anterior extremities 

 like the second nerve from the ganglions of the centipede. The 

 elytral ganglion, or the third of the ventral series, is larger than the 

 preceding one. Viewed from the dorsal aspect, it is seen to distribute 

 three small nerves to the muscles of the wing-cover ; the posterior 

 branch, anastomosing with the nerve sent from the succeeding gan- 

 glion to the wing, thus serves to combine these organs of flight in 



