312 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



this anterior branch of the dorsal nerve becomes the anterior wing 

 nerve {AWNv) and enters the tegmen. 



The dorsal nerve next provides a large posterior branch which 

 passes mediad of the tergal promotor of the coxa (89) and first ter- 

 gal remotor of the coxa (90) to become the posterior wing nerve 

 (PWNv). The dorsal longitudinal muscle (81) and the oblique dor- 

 sal muscles (82) receive innervation from the main part of the dorsal 

 nerve, which terminates in a fine branch to the aorta (HNv). A simi- 

 lar lateral innervation of the dorsal vessel of the cockroach was de- 

 scribed by Alexandrowicz (1926). 



The dorsal longitudinal muscles of an insect segment are among 

 the most important morphological "landmarks" in a segment, since 

 their points of attachment may often be used to identify the true 

 intersegmental lines of the primary segment. This use is, in fact, 

 recognition of the antiquity of these muscles as elements of arthropod 

 structure as ancient as the segments themselves. If this concept is 

 true, it follows that the nerves to those muscles must have a corre- 

 sponding phylogenetic antiquity, and that the elements of these nerves 

 which innervate the dorsal longitudinal muscles in both thorax and 

 abdomen are homologues. 



The muscle-nerve patterns of the pregenital abdominal segments 

 of Dissosteira (exclusive of the first and second abdominal segments) 

 and of certain other Orthoptera were described by the writer 

 (Schmitt, 1954). A comparison of the nerve entering the dorsal 

 longitudinal muscles of such an abdominal segment with the nerve 

 to the corresponding muscles of the mesothorax reveals a number of 

 points of similarity. The abdominal segment muscle-nerve pattern of 

 Dissosteira is shown in diagrammatic form in figure 5 A. 



The first point of similarity involves the presence of an anterior 

 branch of the a1)dominal dorsal nerve from which a branch provides 

 innervation of the spiracular muscles. This pattern was discovered 

 in Acheta, Periplaneta, and Diapheromera, as well as in Dissosteira. 

 In the mesothorax of Dissosteira, the spiracular muscles (79, 80) 

 similarly receive a branch which arises from the nerve that innervates 

 the dorsal longitudinal muscles (fig. 2). 



A second point of similarity involves the median or unpaired nerv- 

 ous system in the abdomen and its connections with the branch of the 

 dorsal nerve passing to the spiracular muscles, as shown in figure 

 5 A, B. The transverse branches of the median system in Acheta, 

 Periplaneta, and Diapheromera, as well as in Dissosteira, join this 

 anterior branch of the dorsal nerve. In the mesothorax of Dissosteira 

 (fig. 2) no definitive median nerve occurs, but the transverse nerves 



