NERVOUS SYSTEM OF GRASSHOPPER — SCHMITT 325 



comes the anterior wing nerve. This nerve from the prothoracic 

 ganghon evidently is a combination of the transverse nerve and the 

 median nerve elements of its side of the insect. A similar transverse 

 nerve arises from the mesothoracic ganglion and passes to the meta- 

 thoracic dorsal nerve. As in the mesothorax, the muscle of the second 

 spiracle receives a fine nerve from the branch of the dorsal nerve, 

 near the junction of the transverse nerve. The dorsal nerves of the 

 first and second abdominal segments also receive paired nerves from 

 the definitive metathoracic ganglion which are clearly the transverse 

 nerves of those abdominal segments (fig. i). 



In the thorax of Chauliodes, as described by Maki, the transverse 

 nerves, the dorsal nerves, and the innervation of the spiracular 

 muscles present a pattern identical with that in Dissosteira. Moreover, 

 in both insects, there appears to be no essential diflference in the 

 innervation patterns of the thoracic spiracles as compared with the 

 abdominal. It is interesting, also, to note that the innervation pattern 

 of the thoracic and the abdominal spiracles makes a continuous series, 

 showing that the thoracic spiracles clearly belong to the mesothorax 

 and the metathorax. 



Snodgrass (1935) has presented morphological evidence in support 

 of a theory that the thoracic spiracles of the Pterygota are not ho- 

 mologous with the abdominal spiracles of these insects, but evolved 

 independently of the more ancient abdominal spiracles. According 

 to this concept, the Japygidae, possessing three or four pairs of 

 spiracles in the thorax, retain two pairs of spiracles homologous with 

 the abdominal spiracles, and have also two pairs of spiracles cor- 

 responding to the thoracic spiracles of the Pterygota. In view of the 

 fact that in both Dissosteira and Chauliodes, the innervation patterns 

 of the thoracic and abdominal spiracles are so closely similar, it may 

 be questioned whether the pterygote thoracic spiracles arose com- 

 pletely independent of the abdominal. 



The transverse nerve arising from the median nerve between the 

 suboesophageal ganglion and the prothoracic does not join the pro- 

 thoracic dorsal nerve, but terminates on the second cervical nerve. 

 No explanation of this seeming anomaly has occurred to the writer, 

 unless it means that the second cervical nerve involves separated ele- 

 ments of the prothoracic anterior ganglionic connective which in other 

 segments join the dorsal nerve. If the dorsal cervical longitudinal 

 muscles are derived in part from the primitive dorsal longitudinal 

 muscles of the labial segment, this second cervical nerve should pre- 

 sumably be the dorsal nerve of the labial segment. But the attachment 



