NO. I 



INSECT THORAX SNODGRASS 



49 



(iPh, 2PI1, 3PI1) bearing the muscle attachments. At C, a condition 

 is given in which the antecosta of the first abdominal tergum (IT), 

 with its phragma (jPh) and the precosta are separated from the 

 principal part of the abdominal tergum and are more closely con- 

 nected with the tergum of the metathorax (T3). The abdominal pre- 

 costa and antecosta, or the base of the phragma, here constitute, then, 



IPh 



Fig. 22. — Diagram of wing-bearing terga with postnotal plates. 



A, tergal plates of mesothorax ; B, tergal plates of metathorax. Each post- 

 notum (PN2, PAh) consists of precosta (Pc) and narrow postcostal piece 

 detached from following tergum, with a phragma (Ph) developed from the 

 antecostal ridge, the base of which is marked externally by the primarily 

 intersegmental antecostal suture (ac). 



the postnotum (^F A/'aJ of the metathorax. The latter segment is now 

 provided with two phragmata, an anterior phragma (2Ph), and a 

 posterior phragma (sPh), and its dorsal muscles become segmental 

 instead of intersegmental. The relations between the mesothorax and 

 the metathorax are here (C) of the normal type. The condition re- 

 presented is characteristic of the Orthoptera, Euplexoptera, and 

 Coleoptera, though in the first two orders the postnotum of the meta- 

 thorax usually retains its connection with the first abdominal tergum. 



