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



lower margin of the alar area al. It is possible for muscles to 

 shift slightly in certain cases, however, as may be seen by com- 

 paring the muscles attached to the subalar plate in the meso- 

 thorax, with those of the metathorax, in the figures of the mus- 

 culature of Gryllus, by Voss, 1904. At any rate, the location 

 of the plate d? of figure 21 corresponds so closely to that of the 

 typical subalar plate of adult insects, that I have provisionally 

 homologized it with the true subalar plate. On the other hand, 

 the plates labeled d in figures 17, 20, and 23, may not be strictly 

 homologous with plate df of figure 21, but since my material of 

 these insects is too shrunken and poorly preserved to permit a 

 study of the muscles, this point must await further investigation. 



With regard to the true pleural plate ep of figures 18 and 21, 

 which is divided by an internal ridge, or apodeme, and an exter- 

 nal suture, into two regions es and em, it would appear that the 

 plate in question comes to occupy a much greater area in the adult 

 than in the larval condition; so that the region es of figure 18 

 corresponds only in a general way to the episternum of the adult, 

 as es does to the epimeral region of the imago. 



The apodeme of the pleural plate in Gryllus, is connected with 

 the furca by the furca-apodemal muscles. The epimero-subalar 

 and epimero-scutal muscles connect the epimeron with the 

 subalar plate and scutum; and the trochantero-episternal, coxo- 

 episternal, and trochantino-episternal muscles connect the epi- 

 sternum with the trochanter, coxa, and trochantin in Gryllus, as 

 shown by Voss, 1904. 



Tergal Subdivisions. 



The entire dorsal region of a segment, including the more 

 membranous as well as the more heavily chitinized portions, is 

 termed the tergum, or notum. When the longitudinal dorsal 

 muscles are developed, they are usually attached to phrogmas, 

 or transverse shelf-like internal structures of the tergal region, 

 which serve to demark the limit; of the metameres. The alar 

 area ' al' of figures 18 and 21, in which .the wing develops, is 

 tergal in nature, according to Craighead, 1916 a view which is 

 in harmony with the modern conception of the nature of the 

 wings (see Crampton, 1916). 



As pointed out by Verhoeff, 1904, and Snodgrass, 1909, two 

 .principal plates occur in the tergal region. The anterior one of 

 these two plates (en of text-figure and figs. 18, 19, 21, etc.) is 

 usually the only one developed in larval forms, while the posterior 

 plate (psl of text-figure), which is the postscutellum of adult in- 

 sects, usually found in the region psl of figures 22 and 18, when the 

 muscles of flight have developed: to it are attached the prescuto- 

 postscutellar, scutello-postscutellar, and other longitudinal mus- 

 cles, as in GryUns. 



