NERVOUS SYSTEM OF GRASSHOPPER — SCHMITT 313 



of the median system extend from the prothoracic ganglion to the 

 anterior branch of the dorsal nerve. Since these transverse nerves 

 probably contain in their anterior sections some of the same axones 

 vv^hich in the abdomen contribute to the anterior part of a median 

 nerve, it appears that precisely the same association of median nerv- 

 ous system and segmental dorsal nerve exists in the mesothorax as 

 in the abdomen. 



Maki (1936) shows by his illustrations that a similar arrangement 

 of the dorsal nerve and the transverse nerve exists in both the thoracic 

 and abdominal systems of the alder fly, Chauliodes formosanus. The 

 existence of an identical complex in the order Neuroptera shows that 

 this nerve-muscle arrangement is not limited to the Orthoptera, and 

 suggests that it may be of fundamental significance in insect 

 morphology. 



In addition to innervating the dorsal muscles of the mesothorax, 

 the dorsal nerve also provides an anterior branch which enters the 

 tegmen anteriorly (fig. 2, 2 AWN) and a posterior branch, entering 

 the same wing posteriorly (fig. 2, 2PWN). Maki found in Chauliodes 

 a nerve, his "fourth root," arising from the anterior part of the meso- 

 thoracic ganglion and passing directly, without innervating any mus- 

 cles, into the wing. Presumably these wing nerves in Dissosteira and 

 Chauliodes are in fact homologous nerves despite the different routes 

 by which they reach the wing. 



III. THE SECOND AND THE THIRD NERVE ROOTS 



Unlike the dorsal nerve, the second pair of nerve roots of the meso- 

 thorax has no connections with nerves outside that segment. This 

 nerve leaves the ganglion and passes under the ventral longitudinal 

 muscles (figs, i, 3 A, //). Its first branch innervates the anterior 

 rotator of the coxa (92) and part of the depressor of the trochanter 

 (103), and a second branch innervates the abductors of the coxa (94, 

 95, 96) . The main nerve passes between the first and the second ter go- 

 sternal muscles (83, 84) and provides innervation for them. The root 

 terminates by innervating the basalar epipleural muscles (97, 98) and 

 the tergal promotor of the coxa (89). 



The third root of nerves is the source of the innervation of all the 

 intrinsic musculature of the leg, as well as of the remaining thoracic 

 muscles exclusive of the ventral longitudinal muscles (figs, i, 3 B, 

 ///). A branch of the third root very close to the ganglion innervates 

 the sternal remotor of the coxa (93), a coxal depressor of the tro- 

 chanter (103), the tergopleural muscle (85), the pleurosternal muscle 



