206 LECTURE XVI. 



in the deflected part of the head. The oesophageal chords are short, 

 uniting in a maxillary 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 dis- 

 tribute three small nerves to the muscles of the wing-cover ; the pos- 

 terior branch, anastomosing with the nerve sent from the succeeding 

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

 action in the Orthopterous insects. In the Coleoptera, whose elytra do 

 not move in flight, this anastomosis of the nerves does not take place. 

 Four pairs of nerves come into view Avhen the elytral ganglion is ex- 

 posed from below : the anterior of these runs forward at an acute angle 

 to the muscles of the first and second pairs of legs. The next two anas- 

 tomose with an alar branch. The third pair enters the second pair of 

 legs, and is disti-ibuted to their terminal segments. The posterior nerve 

 passes to the alar plexus. The substance of the bilobed elytral ganglion 

 seems to be superadded to the under or ventral part of the nervous 

 chord. The alar ganglion, formed by a confluence of the fourth and 

 fifth of the larval ganglions, is situated at the same distance from the 

 elytral as this is from the brachial ganglion. It is not quite so broad 

 as the elytral ganglion, the wings which it supplies being shorter than 

 their covers. The anterior nerve enters into communication with the 

 elytral branches, as does also the second nerve, with the addition of 

 branches to the muscles of the legs. The third nerve is distributed 

 to the third pair of legs ; the fourth to the muscles of the wing. The 

 remaining six ganglions of the ventral series are contained in the ab- 

 domen : they are smaller than the preceding, the distance between 

 them progressively increasing after the third. The last, formed by 

 the confluence of the eleventh and twelftli ventral ganglions of the 

 larva, is of a triangular form, and the largest of the series. It sends 

 off" a pair of conspicuous nerves to the cercse or anal antennae. The 

 two interganglionic columns are in contact lengthwise from the head 

 to the anal ganglion. In the Meloe they are smaller, and separated by a 

 marked interspace. The respiratory nerves may be seen on the dorsal 

 aspect above the second, third, and fourth ventral ganglion. If the 

 nervous system of the Blatta be compared with the stages of deve- 

 lopment of that system in an insect presenting a more concentrated 



