[duporte] LARVA OF SPHIDA OBLIQUA WALKER 229 



portion of the head, immediately above the oesophagus (figs. 1, 3 

 and 7, OE.) and just behind the anterior end of the dorsal vessel 

 (figs. 3 and 7, Ao.) which passes between the oesophagus and the 

 brain. 



The two ovoid ganglia are joined at one side of their bases, the 

 apices, (from which the nerves arise), projecting obliquely forward 

 so that the anterior margin of the brain has somewhat the appear- 

 ance of an inverted ogee arch, while the posterior margin is bi-lobed. 

 The ventral side of the brain is somewhat concave owing to its position 

 on the oesophagus. The commissure between the two halves of the 

 brain has disappeared, but where the two ganglia have grown together 

 there is a distinct linear depression which serves as a line of demarc- 

 ation between them. 



From the supra-oesophageal ganglion the following pairs of 

 nerves originate. (1) The optic nerves, (2) the antennal nerve, (3) 

 the arched and clypeo-labral nerves, (4) the crura cerebri, (5) oc- 

 casionally, the accessory commissure, and (6) the two pairs of nerves 

 which connect the lateral ganglia with the brain. The last and the 

 arched nerve will be described under the sympathetic system. 



The Optic Nerve. (Fig. 3, O.N.) This nerve arises as a large 

 nerve trunk from the lateral edge of the anterior border of the supra- 

 oesophageal ganglion. It runs obliquely forward unbranched, passing 

 above the flexor muscles of the mandibles. It then bends down- 

 wards until it reaches the wall of the head between the third and fourth 

 ocelli. Here the nerve divides, one branch running forward along 

 the wall of the head, the other running backward. From each of 

 these branches three short stout nerves (fig. 3, oc.) are given off, one 

 going to each of the ocelli. 



The Antennal Nerve (figs. 1 and 3, A.N.) arises inside the origin 

 of the optic nerve. This nerve is quite stout but not as large as the 

 optic nerve. It runs side by side with the latter unbranched until it 

 reaches the tentorium. In front of the tentorium it gives off two 

 minute branches (a) which innervate one of the antennal muscles. 

 Branch b is given off in front of branch a. This runs toward the side 

 of the head innervating the seta situated just behind the antenna. 

 The third branch c is a small nerve running towards the centre of the 

 head and innervating antennal muscles. After giving off branch c, 

 the antennal nerve enters a pear-shaped sac which projects into the 

 antenna. Branch d is given off shortly after the nerve enters the sac, 

 and a fifth branch arises farther in. The main branch of the nerve 

 continues into the end of the antenna. 



The Clypeo-Labral Nerve. (Fig. 3, C.L.) This nerve originates, 

 in connection with the arched nerve (Ar.), from the brain just above 



