No. 1774. THORAX OF HYMENOPTERA—SNODGRASS. 55 



others (except the Isoptera), having the wings equally developed, 

 possess a well-developed postnotum back of each wing-bearing plate. 

 In the Diptera and the higher Lepidoptera the postnotum of the 

 metatergum is reduced or obliterated. In the Tenthredinoidea and 

 Siricoidea it is distinct in each segment. In the other Hymenoptera 

 the postnotum of the mesothorax is hidden by invagination within 

 the body, while that of the metathorax is usually fused with the first 

 abdominal tergum. In the mesothorax of the Orthoptera, Euplex- 

 optera, and Coleoptera, where the front wings are developed as pro- 

 tective structures rather than as organs of flight, the postnotum is 

 lacking, or is possibly represented in a very rudimentary condition in 

 a few species by two small plates yoking the mesonotum to the meta- 

 notum. 



The writer (1908, 1909) has heretofore contended that the Orthop- 

 tera have no postnotum in either segment. Crampton (1909) opposes 

 this with the statement that ''the postscutellum of Gryllus domesticus 

 is quite well developed." Other writers, including Voss (1905), have 

 likewise described a postnotum under some name in the metathorax 

 of various members of the Orthoptera, but in all such cases the sclerite 

 referred to is actually, i. e., by anatomical continuity, a part of the 

 first abdominal segment. The present writer has examined species of 

 Gryllus, Gryllodes, and Nemohius and finds that there is in each an 

 anterior subdivision of the apparent first abdominal tergum, to the 

 internal surface of which are attached the posterior ends of some of 

 the longitudinal dorsal muscles of the metathorax, especially two 

 lateral bands. Hence, this may be taken as evidence that the sub- 

 sclerite in question is the true postscutellum or postnotum of the 

 metathorax. It is largest in Nemohius, but is more distinct from the 

 fu'st al)dominal tergum in Gryllus than in the other two genera, while 

 in Gryllodes it is so small and so intimately a part of the abdominal 

 tergum that it certainly taxes one's credulity to believe it is anything 

 else. In Blatella there are two small lobes, situated laterally upon the 

 front edge of the first abdominal tergum, to which are attached the 

 posterior ends of some of the lateral longitudinal muscles of the 

 metanotum. By the same reasoning, as in the case of the Gryllid£e, 

 these lobes may be argued to be rudiments of the metapostnotum in 

 tlie Blattidse. In the Acridiidse the first abdominal tergum presents 

 a large subdivision extending downward on the sides before the 

 lateral tympanna of this segment. A longitudinal section of Tri- 

 merotroims maritima (fig. 12) shows that, to the middle of this appar- 

 ent subdivision (PN^) of the fu'st abdominal tergum (IT), is attached 

 the posterior phragma (SPJi), and that upon this plate and the 

 phragma are inserted the posterior ends of the great dorsal longitudinal 

 muscles of the metathorax (D Mel) . Finally, in the Locustidse (fig. 13) 

 there is a conspicuous arched anterior subdivision (PN^) of the 



