1 90S] Nervous System of the Larva of Corydalis 109 



from the base of the crus cerebri or more generahy dorsad of the 

 base of the crus cerebri. Under no circumstances could this 

 nerve be considered as originating from the crus, since it is a well 

 established fact that the nerve fibres of the labral nerve arise 

 from the tritocerebrum. 



At a distance of from one-half to one millimeter from its point 

 of origin, the clypeo-labral nerve becomes separated from the 

 arched nerve and projects cephalad into the clypeus and labrum, 

 where it breaks up into six branches. The distribution of these 

 is obvious from an examination of figure 4 and need not be dis- 

 cussed in detail. The relation of branch j to the s^aiipathetic 

 system is worthy of note. 



In addition to the above described nerves of the supra- 

 oesophageal ganglia there is to be found a pair of minute nerves 

 which arise near the middle line of the caudal portion of the brain 

 (Fig. 4.) These project dorso-caudad to the roof of the head. 



The Crura Cerebri (Figs. 2, 5, 7, cr). The crura cerebri 

 consists of two large nerve cords connecting the supra- and sub- 

 oesophageal ganglia and with them forming the so-called oesopha- 

 geal ring. Each crus originates from the ventro-lateral border of 

 the brain, turns ventrad around the oesophagus and enters the 

 dorso-lateral border of the suboesophageal ganglion. 



The suboesophageal commissure *(Figs. 2 and 7, s.c). 

 Connecting the lower portions of the crura cerebri, and forming 

 a semicircle round the ventral part of the oesophagus is the so- 

 called suboesophageal commissure. This commissure, usually 

 overlooked, has been found in a number of widely separated 

 insects (for summary see Kolbe '93, pp. 411-413). In the 

 most frequently cited instances this commissure originates from 

 the brain, although a position similar to that of the Corydalis is 

 reported for Libellula, Dytiscus, Carabus, Phryganea and various 

 other insects. 



From the suboesophageal commissure there are two cephalad 

 projecting nerves, which innervate the upper longitudinal labial 

 muscles (Fig. 2, Im). 



* Various names have been applied to this commissure. Thus, Lienard 'SO 

 calls it : Les connexions transversates des commissures oesophagicnncs ; Kolbe '93 

 Qiiercoinmissure or Schlundring; Edward Burgess '80 : Cross-nerve or commissure 

 between the two hemispheres; while Packard '98 refers to it as transverse comniissitre 

 of the oesophageal ring. Since these terms are applicable only in limited groups 

 it is preferable to use the term suboesophageal commissure. 



