182 PROC. ENT. SOC. WASH., VOL. 23, NO. 8, NOVEMBER, 1921 



(Plate XV, figs. 16, 17 and 18). Scutellum (including posttergite 1 ) 

 is formed under the subdorsal pair of discs of C, and area D is 

 above the posterior of scutellum and the membrane separating 

 postscutellum from the anterior portion of the mesothorax. 

 Postscutellum is found under area A of the prepupa's metathorax 

 which occurs in the depression between the mesothorax and the 

 metathorax. The metathoracic scutum and scutellum are 

 below areas B and C. The scutum being found below area B 

 and the latero-dorsal and supraalar discs of area C and the 

 scutellum being found below the subdorsal discs of area C which 

 are rather distinct from the remainder of C. Metathoracic area 

 D is very narrow and area A of the first abdominal tergite is 

 above the postscutellum of the metathorax. , 



The phragmae seem to be the prolongations of the infolded 

 margins of areas used for attachment of the muscles which have 

 been enlarged. In their development, the particular muscles 

 enlarged, for the accomplishment of the new duties or activities 

 required of the insect upon reaching its adult stage, are the con- 

 trolling guide. Area A in bearing on its posterior and anterior 

 margin all the attachments of intersegmental muscles (Plate 

 XIV, fig. 3) is the natural base for these structures as evinced 

 by the following text figure and the illustration showing the 

 longitudinal section of the adult mesothorax (Plate XV, fig. 22). 

 An examination of these drawings will show the anterior margin 

 of the prescutum (or A larval mesothorax) and the posterior 

 margin of the postscutellum (or A larval metathorax) produced 

 to form phragmae and connected by a large muscle. An exami- 

 nation of the drawing of Pteronidea ribesii musculature will reveal 

 that there exists already in the larval thorax (T III Plate XIV, 

 fig. 3) three muscles having these points of attachment in 

 common. 



From the above comparison, which describes the position 

 occupied by the tergal sclerites of the adult in relation to tergal 

 areas of the prepupa, it would seem that the adult tergal sclerites 

 are developed from the larval areas indicated in the following 

 table and figure. 



Suggested Homologies. 







Adult and Pupa from Prepupa and Larva. 



Pronotum B and C prothorax 



Membrane between pronotum and 



prescutum D prothorax. 



'The posttergite is the "lobe on posterior margin of scutellum" recognized 

 by Snodgrass ("Thorax of Hymenoptera," Proc. U. S. X. M., Vol. 3'^, pp. 37-91. 

 See o, page 88 and Plate T, fig. 3) and designated "posttergite" by Crumpron 

 ("The Ground Plan of a Typical Thoracic Segmcnr in \Vinged Insects, " 

 Zoologischer Air/eiger, Vol. 44, 1914, pp. 56-67. See page 60.) 



