6 Psyche [February 



region "psc" demarked in both segments (Figs. 1 and 3), and 

 situated well in advance of the wing bases, while the prescutal 

 region is not so clearly demarked in the Coleoptera and Dermap- 

 tera (Figs. 2 and 4), and, when present in the latter insects, it is 

 situated on a line with, or back of, the wing bases (or rather the 

 anterior margin of the wing bases) . 



In the Plecoptera and Embiids, there is a well developed mes- 

 othoracic postscutellum ("psl2"), while the mesothoracic postscu- 

 tellum is not developed in the Coleoptera and Dermaptera, nor 

 does the metathoracic postscutellum ("psls") dip downward at such 

 a marked angle in the Coleoptera and Dermaptera (Figs. 2 and 4) 

 as in the Embiids and Plecoptera (Figs. 1 and 3). The tegula 

 ("tg") is well developed in both segments in the Embiids and 

 Plecoptera (Figs. 1 and 3) while it seems to be lacking in the Cole- 

 optera and in the metathorax of the Dermaptera, although the 

 mesothoracic sclerite labeled "tg" in Fig. 4 is interpreted as the 

 tegula in the Dermaptera, by Pantel, 1917, in his excellent mono- 

 graph of the thoracic region of these insects. 



In the Coleoptera (Fig. 2) a myodiscus, or muscle disk "d, " to 

 which are attached certain muscles connected with flight, occurs 

 in the metathorax, and might be mistaken for the tegula. It is 

 homologous with a smaller disk labeled "d" in the metathorax of 

 the Dermaptera (Fig. 4, "d") which corresponds to the small disk 

 "d" near the tegula "tg" of the mesothorax of the same insect 

 (Fig. 4) ; and a similar small disk "d" occurs near the tegula in both 

 mesothorax and metathorax of Plecoptera (Fig. 1). Snodgrass, 

 1908, in his earlier work, which was incorporated in his more exten- 

 sive studies of the thoracic sclerites and wing bases of insects 

 (Snodgrass, 1909) refers to the sclerite in question as the "muscle 

 disc" in Coleoptera, but does not seem to have found it in other 

 insects. Pantel, 1917, interprets the sclerite "d" in the meta- 

 thorax of the Dermaptera (Fig. 4) as an intersegmental plate. 



The terms axillaries, alar ossicles, and pteralia, have been applied 

 to the little plates by means of which the wings articulate with the 

 tergal region, and in a paper dealing with the nature and origin of 

 the wings of insects (Crampton, 1916) it was pointed out that the 

 alar ossicle "np" (termed the notopterale) is probably a detached 

 portion of the notum or tergal region of the segment. A further 

 examination of these alar ossicles would tend to confirm this sup- 



