60 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



phragma. Consequently, in the case of the mesothorax a post- 

 notum is present in most cases only when the middle phragma is 

 present and attached to the mesotergum; in the case of the meta- 

 thorax, a postnotiim is present in most cases only when the posterior 

 phragma is present. The anterior phragma being never attached 

 to the protergimi, the prothorax never possesses a postnotum. The 

 postnotum is lacking in the mesothorax of Orthoptera, Euplexoptera, 

 and Coleoptera, in which orders the middle phragma is attached to 

 the front of the metatergum. It is greatly reduced or obliterated in 

 the metathorax of the Diptera and in most of the higher Lepidoptera, 

 which have but a weakly developed posterior phragma or none at 

 all. On the other hand, it is present in both segments of the Epheme- 

 rida, Odonata, Plecoptera, Corrodentia, Neuroptera, Trichoptera, and 

 the lower Lepidoptera, while it is well developed in the mesothorax 

 of the higher Lepidoptera, and reaches its greatest size in the meso- 

 thorax of the Diptera, which have an extremely large middle phragma 

 attached to this segment. In the Tenthredinoidea and Siricoidea of 

 the Hymenoptera it is well developed in each segment; in the other 

 Hymenoptera the postnotum of the mesothorax becomes buried 

 between the segments, while that of the metathorax fuses with the 

 first abdominal tergum. 



If, now, we compare this distribution of the postnotum through 

 the various orders with the development of the wings, it at once 

 becomes evident that the postnotum is present in those segments 

 that have the wings developed as organs of flight and that its size 

 varies directly with the development of the power of flight. Thus, 

 the front wings of the Orthoptera, Euplexoptera, and Coleoptera are 

 developed principally as protective organs, while in the higher Lepi- 

 doptera and Hymenoptera they are the principal, and in the Diptera 

 the only, organs of flight. In the other orders that use the two 

 wings more equally, the postnotal plates are about equal in the two 

 segments, except the Isoptera, which, as has already been stated, do 

 not possess a postnotum in either segment." 



The Ilemiptera appear to be somewhat contradictory to the above 

 statements in some ways. Belostoma, for example, and probably all 



a Each wing-bearing tergum of the Isoptera consists of only one plate which, though 

 in some cases almost cut by the deep lateral emarginations into two parts, the "ante- 

 dorsum" and "postdorsum" of Enderlein (1903), is yet clearly the notum because of 

 the wing attachments to it. The writer has examined representatives of Termopsis, 

 Calotervies, Copritermes , Microtermes, Armitermes, and Eutermes but has found no 

 trace of a postnotum in either segment. A very small set of dorsal longitudinal 

 muscles is present attached to the front and rear of each segment, just as in the stonefly 

 nymph. On the other hand the lateral dorso-ventral muscles are very large and 

 extend from the anterior part of the notum to the epimeral plate of the coxa on each 

 side. Each coxa has the appearance of being double — a distinctive character of the 

 Neuroptera, Mecoptera, Trichoptera, and Lepidoptera. This and the absence of the 

 postnotal plates would separate the Isoptera from the Corrodentia, with which they 

 are frequently associated. 



