June — July 1SS4.J 



PSYCHE. 



181 



They arise from the ventro-latero-ce- 

 plialad portions of tlie supra-oesophageal 

 ganglia, and extend ventrad, joining the 

 snb-oesophageal ganglion at its doi'so- 

 latero-cephalad borders. They are sim- 

 ilar in ontline and appearance to the 

 commissures of the bpdj'. They pre- 

 sent a convexity laterad and a concavity 

 mesad, corresponding to the cylindrical 

 outline of the oesophagus. 



The crural nerves. — At the points 

 of departure of the crura cerebri from 

 the supra-oesophageal ganglia, each cms 

 gives ort" two nerves, the vagus and the 

 clypeo-labral (fig. i. 2, 3 and fig. iv. S, 

 9). The vagus nerve will be described 

 later as a special part of the nervous sys- 

 tem of the head. 



The clypeo-labral ncri'cs. — The cly- 

 peo-labral nerves, two in nmnber, arise 

 one from each crus near its origin (fig. 

 I. 3). They extend cephalad and a little 

 mesad. Each gives otf" three small 

 liranches in the clypeus, and a fourth, 

 long branch whicii extends cephalad to 

 tlie base of the labrum and penetrates 

 the integument. After giving ofl' these 

 branches, the main trunk extends cepha- 

 lad into the labrum and may be termed 

 the labral nerve. This labral nerve di- 

 vides into several small branches near 

 the tip of the labrum. The largest of 

 these branches enters a labral palpus ( .''), 

 or probably a seta. 



The crura cerebri are joined together 

 by a cord of nerve matter (fig. vii. 3) 

 one-half millimetre from their attach- 

 ments to the sub-oe.sophageal ganglion. 

 This cord or cross-nerve of the commis- 

 svu'es is dorsatl cjf the cephalad pait of 



the sub-oesophageal ganglion, and is 

 entirely concealed by it. The cross- 

 nerve arises from the commissures and 

 like the commissures follows the outline 

 of the oesophagus, presenting a convex- 

 ity ventrad, and a concavity dorsad. 



3. The sub-oesophageal gan- 

 glion, OR CEREBELLUM. — The sub-oes- 

 ophageal ganglion (fig. 11. i) is situti- 

 ted in the ventro-cephalad part of the 

 head, midway between the tips of the 

 labium and the base of the head. It 

 lies ventrad of the oesophagus, and is 

 separated from the ventral body-wall by 

 a layer of muscles and by adipose tissue. 

 The sub-oesophageal ganglion, the prob- 

 able homolog of the verteinate cere- 

 lielhmi, differs somewhat from the other 

 ganglia. It is iiearly cordate in outline, 

 with two apices pointing caudad and 

 terminating in the commissures. Its 

 cephalo-caudal diameter is one and one- 

 half millimetres, and its greatest width 

 is one millimetre, in the two-year-old 

 larva. It is connected to the supra-oes- 

 ophageal ganglia by the crura cerebri, 

 and to the other ganglia of the body by 

 the commissures. It is covered with a 

 thin, delicate curtain-membrane, the 

 neurilemma. 



Tracheae also penetrate the body of 

 the ganglion, ramifying to all parts. 



The cerebellar nerves. — The cerebel- 

 lar nerves consist of a pair each of labial, 

 gustatory, maxillary, and mandibular 

 nerves, and three other, unnamed pairs 

 of nerves. 



The labial nerves. — The labial 

 nerves (fig. n. 3) originate from the ven- 

 tro-latero-ceplialad borders of the sub- 



