NO. 



INSECT ABDOMEN — SNODGRASS 



the sides of the scgnieuts ahovc the regions of the hmh bases, and 

 therefore in the lateral parts of the dorsum (figs. i. 2 \, Sp). If 

 the tergal sclerotization of a segment does not invade the spiracular 

 areas, the spiracles commonly lie in membranous lower parts of the 

 dorsum between the tergum and the limb bases (fig. 2 A ) , or between 

 the tergum and the definitive sternum, which has absorbed the limb 

 bases (B). The tergal plates of the abdomen, however, often extend 



Fig. 2. — Diagrams showing the sclerotization and the retractor mechanism of 

 the abdomen. 



A-E, variations of sclerotization above and below the dorso-pleural line (a-a) 

 separating the dorsum from the region of the limb bases (LB). F, the retractor 

 mechanism as seen in vertical section, resulting from secondary segmentation 

 produced by the usual type of sclerotization in adult insects. G, two consecutive 

 segmental plates and their connecting muscles. 



a-a, dorso-pleural fold; Ac, antecosta ; acs. antecostal suture; DMcl, dorsal 

 longitudinal muscles; Isg, primary intersegmental fold; LB, limb basis; Mb. 

 secondary intersegmental membrane; McI, longitudinal muscle; patg, parater- 

 gite ; Pc, precosta ; PI, pleural plate formed of the limb basis ; S, definitive ster- 

 num including areas of limb bases ; Sp, spiracle ; Stn, primary sternal plate ; 

 T, tergum. 



SO far downward on the sides of the dorsum as to include the spiracles 

 in their lateral parts (C). In some cases the spiracles occur in inde- 

 pendent lateral, or paratergal, sclerites of the dorsum (D). Finally, 

 the definitive ventral sclerotization is sometimes produced upward 

 on the sides of the abdominal segments, and the spiracles may then 

 be included in the lateral parts of the sternal plates (E) ; but in such 

 cases it is to be suspected that the apparently sternal areas containing 



