FORM, GROWTH, AND CHANGE 13 



cms than in the grasshopper. In the sternal or lower (ventral) 

 area of a thoracic segment, the bilobed central sternum (Fig. 5 

 5) is the most prominent sclerite, behind this is a post-sternum 

 (Fig. 5 Psl) and on either side, extending to the insertion of the 

 leg an episternum (Fig. 5 Eps) this latter together with an epi- 

 meron (Fig. 5 Epm) lying behind it, reaches upwards to the base 

 of the wing in the mesothorax and metathorax, forming the 

 pleural area of the exoskeleton. 



FIG. 5. DIAGRAM OF INSECTAN MESOTHORAX (side view). 



Psc, prescutum ; Set, scutum ; Scl, scutellum ; Pscl, post- 

 scutellum ; Aph, Pph, phragmata for muscle attachment ; 

 Anp, Pnp, notal wing processes; WP, pleural wing process; 

 i. a. s. 4 P, basal wing-sclerites ; Peps, pre-episternum ; Eps, 

 episternum ; Epm, epimeron ; Ps, pleural suture ; CxP, coxal 

 process ; Cx, coxa (haunch) of leg ; Tn, trochanteria ; 

 Tnc, its coxal articulation ; Ps, presternum ; S, sternum ; 

 SI, sternellum ; Psl, poststernum. After Snodgrass, U.S. 

 Dept. Agric. Entom. Tech. Ser. XVIII. 



Each segment of the thorax carries a pair of legs, the leg 

 being inserted on either side between the sternal and pleural 

 regions. The leg (Fig. 6 A) is a beautifully jointed organ built 

 up of a series of sclerites united by short tracts of flexible cuticle. 

 The basal segment is a stout haunch (coxa) linked by a 

 small trochanter to the long thigh (femur), to which at the 

 knee-joint is attached the spiny shin (tibia) ; at the far end 

 of this comes the foot (tarsus), which in the grasshopper is 



