180 



J'SrCNE. 



[ June— July 1SS4. 



dad border of the supni-oesophageal 

 ganglia on the meson. The opening of 

 the aorta appears as is shown in the 

 phite, fig. I. 7, the dorsal wall having a 

 forked opening near the attachment of 

 the aorta to the neurilemma. 



The supra-oesophageal ganglia are 

 supplied by two large tracheae lying 

 jDarallcl to the oesophagus (fig. iv, 4) . 

 Each trachea sends three branches to 

 the ventral side of each hemisphere. 

 These branches divide and sub-divide, 

 ramifying to all parts of the hemispheres 

 (fig. iv). The supra-oesophageal gan- 

 glia are covered with a thin, delicate 

 curtain-membrane, the neurilemma. 



The cerebral nerves. — The cerebral 

 nerves consist of two trunks of nerves, 

 which originate from two tracts at the 

 lateral apices of the supra-oesophageal 

 ganglia. The cephalad tract gives rise 

 to the antennal nerve, and also a small 

 integumentary nerve, and may therefore 

 be called the antennal tract. The caii- 

 dad tract gives rise to tlie optic nerves, 

 and may therefore be called the oj)tic 

 tract. 



The aiitc7i7ial nerve. — The antennal 

 nerve (fig. i. 4) arises from the anten- 

 nal tract. It extends laterad a distance 

 of one and one-half millimetres, and 

 divides into a cephalad and a caudad 

 branch. 



The cephalail branch (fig. i. 4. (t) 

 continues its course laterad, then ceph- 

 alad, and enters the antenna, supplying 

 it with nerves. It is therefore, prob- 

 ably, the tactile or sensor nerve of the 

 antenna. 



The caudad Imuich (fig. i. 4. h) con- 



tinues laterad, and enters the muscles o'" 

 the antenna in the head (fig. i. 9). At 

 the point of entering the muscles it di- 

 vides into several small branches. This 

 nerve is probably the motor nerve of the 

 antenna. Another small nerve (fig. i. 

 4. c) arises from the antennal tract, and 

 extends laterad a distance of two milli- 

 metres ; it then tll\ ides into two branch- 

 es. These branches pass dorsad of the 

 antennal muscles, and enter the integir 

 ment near the retinas of the e^'es. 



The optic nerves. — The optic trinik 

 of nerves (fig. I. 5) arises from the optic 

 tract. This trunk extends laterad a 

 short distance and divides into seven 

 distinct branches, the optic nerves. 

 These branches continue their course 

 laterad, and are distributed one to each 

 of the seven retinas. It is an interesting 

 fact, that although there are seven ret- 

 inas, the external i)arts of only six 

 ocelli are develo[)ed. l"he presence of 

 the seventh retina and optic nerve can- 

 not be doubted, as it was observed in 

 many specimens of the one- and two- 

 year-old larvae. Fig. vi shows the 

 separation of the optic trunk into the 

 seven optic nerves. J'lie optic and an- 

 tennal nerxes are protected by a cover- 

 ing, the extension of the neurilemma 

 or theca (fig. Vi. 3) which covers the 

 sub- and supra-oeso])hageal ganglia and 

 nerves. 



3. The crura cerebri. — The cr ira 

 cerebri or the cerebro-cerebellar com- 

 missures (fig. IV. 3 and fig. VII. 2) arc 

 two cords of nerve matter connecting 

 the sub- and supra-oesophageal ganglia, 

 and witli them encircle the oesophagus. 



