326 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



of the transverse nerve to the second cervical nerve becomes then 

 even more strange, unless we are to suppose that axones from the 

 transverse nerve cross to the prothoracic dorsal nerve (by means of the 

 anterior branch of the prothoracic dorsal nerve) which joins the sec- 

 ond cervical nerve. Maki mentions a median nerve issuing from the 

 suboesophageal ganglion in ChauHodes, but unfortunately he does not 

 describe its connection sufficiently to permit comparison with Dis- 

 sosteira. Speculation on the significance of this feature of the nervous 

 system is probably futile until further information can be obtained. 

 In the abdomen of Dissosteira, a "ventral nerve" leaves the ganglion 

 posterior to the dorsal nerve, passes beneath the ventral longitudinal 

 muscles, and proceeding laterally and posteriorly, passes laterad of the 

 sternal apodemes to join the anterior branch of the dorsal nerve of 

 the next posterior segment (fig. 5 A, VN). The transverse nerve 

 terminates on this ventral nerve-anterior branch loop. In Diaphero- 

 mera (fig. 5 B) the ventral nerve does not join the anterior branch 

 of the dorsal nerve, but the transverse nerve does. Maki found a 

 ventral nerve in ChauHodes, but as in Diapheromera, it does not join 

 with the dorsal nerve. Although this ventral nerve-anterior branch 

 loop was found in Acheta and Periplancta, it evidently is not an es- 

 sential feature of the abdominal nervous system. The thoracic nervous 

 system of Dissosteira does not appear to possess any nerve patterns 

 suggestive of the abdominal ventral nerve. 



X. THE DEFINITIVE METATHORACIC GANGLION 



It has long been recognized that the ganglion in the metathorax in 

 Dissosteira and in many other Orthoptera contains certain abdominal 

 ganglionic centers as well as the true metathoracic ganglion. In Dis- 

 sosteira the abdominal ganglia involved are those of the first three 

 segments. The various nerves leaving the definitive metathoracic 

 ganglion and serving these segments are shown in figure i, with the 

 exception of the ventral nerves of the left side, which are omitted 

 to reduce the complexity of the figure. The musculature of the abdo- 

 men was described by Snodgrass (1935). 



As previously noted, the muscles of the pregenital abdominal seg- 

 ments in Orthoptera are served by two main nerves, a dorsal nerve 

 {DN) and a ventral nerve {VN) (fig. 5). The dorsal nerves of the 

 first abdominal segment leave the ganglion laterally and just pos- 

 terior to the metathoracic third root (fig. i). A branch of the dorsal 

 nerve innervates the median internal ventral muscle (143) and the 

 lateral internal ventral muscle (144). The main dorsal nerve con- 



