PROC. ENT. SOC. WASH., VOL. 20, NO. 3, MAR., 1918 53 



I 



Berlese, 1909, on the other hand, maintains that the trochantin 

 is a lateral portion of the "sternellum;" but there seem to be no 

 adequate grounds for maintaining this view. 



The trochantinal plate tn, of figure 18 is not the exact equivalent 

 of the sclcrite designated as tn in figures 21 and 15, since the 

 anterior portion of the region tn marked off by a dotted line in 

 figure 15 (which is demarked by a well defined suture in some 

 Plccopteron nymphs) corresponds more nearly to the plate tn 

 of figure 18. For the sake of convenience, however, the sclerites 

 labeled tn in the different figures will be referred to simply as 

 the "trochantin." In the 'thorax of Gryllus, the trochantin is 

 connected with the episternum and with the praesternum by the 

 trochantino-episternal and the trochantino-prescutal muscles. 



The trochantin (or eutrochantin) and the pleura! plate (which 

 is divided by an approximately vertical suture in most of the in- 

 sects studied figs. 2, 9, 12, 13, 15, 18, 19, etc.) apparently repre- 

 sent the original sclerites of the pleura! region, since they are 

 present in many Apterygotan and larval Pterygotan insects. 

 In certain larval forms, however, there occur in the pleura! 

 region several other sclerites whose homologies and phylogenetic 

 significance are not always clear. Thus, in the mesopleural 

 region of the Tenthredinid larva shown in figure 17, there occurs 

 a true pleura! plate ep divided by the typical suture as in the 

 larva of Corydalis (fig. 18, ep) and other lower forms. In the 

 Tenthredinid larva, however, in addition to the true pleura! 

 plate (fig. 17, ep) there occurs a sclerite labeled pp which bears 

 no suture, and is situated immediately above the coxa. Simi- 

 larly, in the Lepidopteron larva shown in figure 20, there occm> 

 a siircoxal plate labeled pp, which bears no typical suture, and is 

 also situated immediately above the coxa, while in the Panorpid 

 larva shown in figure 23 a non-suture-bearing plate labeled pp 

 is found immediately above the narrow band ex! (which 7 apparentlv 

 represents the chitinized portion of the coxa of the Lepidopteron 

 larva, fig. 20, ex). The various sclerites labeled pp in figures 

 17, 20, and 23, may not be strictly homologous in every case, 

 but the correspondence is sufficiently close for all practical 

 purposes. 



In the mesothorax of the Calosoma larva shown in figure 18, 

 there occurs immediately below the alar area <il a distinct plale 

 labeled d?, which, from its position immediately below the wing- 

 region, appears to be homologous with the xiilxilar pln/c of adult 

 insects. Mr. Craighead informs me that the muscles which nor- 

 mally extend between the coxa and the subalar plate (i.e., the cox<>- 

 subalar muscles of such insects as Grylli<*) are not attached to 

 the plate d? (of fig. 21), but extend to a point above it, along the 



