52 PROC. ENT. SOC. WASH., VOL. 20, NO. 3, MAR., 1918 



pleural region, and extending in front of the coxae. In the 

 prothorax of the Plecopteron Capnia (fig. 14) that portion of the 

 connecting bridge which is of strenal origin (i. e., Is of fig. 14) is still 

 attached to the basisternum 6s; but in the mesothorax of a nymph 

 of the Plecopteron Perla (fig. 15) it becomes detached to form 

 the distinct sclerite Is, as is also the case in the Forficulid Arix- 

 enia ,(fig. 13, Is}. In the adult stages of Perla, however, it is 

 still united with the basisternal region. 



As shown by Voss, 1904, in the thorax of Gryllus, the apodeme 

 of the pleural plate is connected with the furca of the sternal 

 region by the furco-apodemal muscles. Epimero-subalar and 

 epimero-scutal muscles connect the epimeron with the subalar 

 and scutal regions, while the trochantero-episternal, coxo-epi- 

 sternal and trochantino-episternal muscles connect the trochanter, 

 coxa, and trochantin, with the episternum. 



As pointed out in a recent paper (Crampton, 1917 a), in prac- 

 tically all of the thoracic segments of Apterygotan insects (fig. 

 12), and in the prothoracic region of the most primitive of the 

 Pterygotan insects, such as the Plecopteron Capnia (fig. 14), 

 the Embiid Embia, the Grylloblatticl Grylloblatta, the Forficulid 

 ' Echinosoma, the Blattid Blaberus, the Phasmid Simema, the 

 Mantid Stagmomantis, various Isoptera, etc., there intervenes 

 between the true pleural plate ep and the coxa ex a plate labeled 

 et (in figs. 12, 14, etc.), which has been designated as the eutro- 

 chantin, or true trochantin (figs. 12, 24 and 25, et shaded in all 

 figures). As seen in figure 25, the shaded eutrochantin breaks 

 up into an anterior portion labeled tn, which remains distinct 

 to form the plate commonly called the trochantin in higher 

 insects, while the posterior portion unites with the pleural plate 

 above it to form the lower portion of the episternal and epimeral 

 regions. The steps in the process of the fusion of the posterior 

 portion of the eutrochantin with the pleural plate are admirably 

 shown in a series of illustrations of the sclerites of Dennaptera 

 recently published by Pantel, 1917. As shown in plate III of 

 Pantel's extremely important monograph, the posterior portion 

 of the eutrochantin, which is distinct in Allostethus, Echinosonni, 

 etc., becomes partially united with the pleural plate in Labidura, 

 though still partially demarked by an incomplete "fissure divi- 

 sante," while in Anisolabis and Calocrania only the faintest 

 traces of the "fissure divisante" are retained, the fusion being 

 practically complete in the latter insects. 



The plate et of figs. 24 and 25 may possibly represent a basal 

 portion of the leg (since certain embryologists maintain that the 

 trochantin is a basal segment of the leg) or it may have had an 

 origin similar to that of the pleural plate ep mentioned above. 



