NERVOUS SYSTEM OF GRASSHOPPER — SCHMITT 319 



The second cervical nerve and the prothoracic and the mesothoracic 

 dorsal nerves are joined by a definitive nerve which extends from 

 the innervation of the sternopleural intersegmental muscle (59) into 

 the cervix, passing mesad of the dorsal nerve of the prothorax, and 

 joined to it by a short connection. A branch from the second cervical 

 nerve marks the anterior end of this definitive nerve. 



The fact that the sternopleural intersegmental muscle (59) receives 

 its innervation from the anterior branch of the mesothoracic dorsal 

 nerve indicates that it should be considered a mesothoracic muscle 

 rather than prothoracic. In Chauliodes, as described by Maki, there 

 exists a similar muscle, the first sternopleural (122), which is inner- 

 vated in exactly the same manner from the dorsal nerve of the meso- 

 thorax, but no anterior extension of the nerve into the cervix exists 

 as in Dissosteira. 



The remaining muscles innervated by the dorsal nerve of the pro- 

 thorax include the protergal muscles of the cervical sclerites (52, 53), 

 although the innervation of one of these muscles (52) could possibly 

 come from the second cervical nerve. The first ventral longitudinal 

 muscle (55) is also innervated by the prothoracic dorsal nerve. The 

 protractor of the crop (46), listed by Snodgrass among the pro- 

 thoracic muscles, is innervated from the ingluvial ganglion. 



A very small and insignificant muscle, not figured by Snodgrass 

 and absent in some specimens, extends from the postocciputal ridge 

 to the first cervical sclerite. It is extremely doubtful that this muscle 

 has any utility or function, hence it is here designated simply by posi- 

 tion as the postocciputal-cervical plate muscle (fig. 2, p-cv). The first 

 cervical nerve passes mesad of this muscle and continues dor sally 

 to enter the cervical integument. The second cervical nerve also passes 

 mesad and provides a small nerve to it. 



The second root of nerves in the prothorax innervates six pairs 

 of muscles. Only three pairs of these may be homologized with 

 muscles innervated by the second root in the mesothorax. These in- 

 clude the following : (i) The tergal promotor (62) ; (2) the abductor 

 of the coxa (68) ; (3) two parts of the depressor of the trochanter 



(71)- 

 The writer believes, however, that consideration of the muscles 



innervated by the third root, together with the fact of the innervation 

 of these muscles by the second root, suffice to show that an organiza- 

 tion of these segmental nerves into an anterior root and a posterior 

 root exists in the prothorax as well as in the pterothorax. It appears 

 also that the evolution of the cervix, with a consequent modification 

 and loss of the anterior musculature of the prothorax, accounts for 



