230 THE ROYAL SOCIETY OF CANADA 



the crus. From its origin the common nerve trunk curves outward 

 and forward and then inward. The two nerves then separate, the 

 clypeo-labral running forward to innervate the clypeus and labrum. 

 In front of the point of separation the proximal branch a is given off 

 from the ventral surface of the nerve. This branch runs around the 

 oesophagus and on the ventral side projects forward to the base of the 

 labium. Branch b goes inward to the large elevator muscles of 

 the labrum, also sending a branch to the pharyngeal muscles. Branch 

 c is given off immediately anterior to b. It too runs inward, entering 

 a minute ganglion-like enlargement (gl) of the frontal nerve of the 

 median sympathetic system. The clypeo-labral nerve bends a little 

 outwards at the origin of branches b and c and runs forwards toward 

 the anterior end of the head. * The fourth branch d innervates the 

 base of the clypeus. Branches e and / innervate the flexor muscles 

 of the labrum. The next branch originates distad of /, and divides 

 into three nerves which innervate the lateral portion of the labrum. 

 The eighth branch curves inward, and running back a short distance, 

 it bifurcates, the two branches going to the posterior portion of the 

 labrum. Branch k also runs inward and bifurcates, innervating 

 certain of the labral muscles. The clypeo-labral nerve then con- 

 tinues its course to the anterior portion of the labrum where it divides 

 into several branches. 



The Crura Cerebri (Figs. 3, 4 and 7, Cr.) These are two stout 

 connectives which are given off from the ventral side of the supra- 

 oesophageal ganglion just behind the origin of the foregoing nerves. 

 They run around the oesophagus and enter the anterior lateral borders 

 of the sub-oesophageal ganglion. 



Together with the ganglia which they connect, the crura cerebri 

 form the so-called oesophageal ring (fig. 7). 



The Accessory Commissure. (Figs. 7 and 8, sc). This is a 

 Commissure which passes beneath the oesophagus and connects the 

 two crura. From the middle point a branch is given off which runs 

 forward along the median line of the ventral surface of the oesophagus. 

 This branch soon bifurcates, sending nerves to two long labial muscles 

 which lie beneath the oesophagus. 



The origin of this Commissure varied considerably in the material 

 examined. In most cases it arose from the crus near the ventral sur- 

 face of the oesophagus; in a few cases it originated from the brain 

 close to the origin of the crus; and in other specimens it arose from the 

 crus at any point intermediate between the two points of origination 

 mentioned above. Hammar describes it in the larva of Corydalis 

 cornula L. as connecting the lower portions of the crura, and, as just 

 stated, I found this to be true in the larva of Sphida obliqua in the 



