INSECT ABDOMEN SNODGRASS 



43 



are not styli, as is suggested anatomically by their lack of muscles. 

 In a female nymph of a cockroach small processes occur on the ends 

 of the limb base lobes of the ninth segment, which almost certainly 

 are true styli (fig. 25 B, Sty) ; they persist, Walker says, until the 

 last molt, but they are not retained in the imago. In the adult roach, 

 however, the outer processes (limb bases) of the ninth segment are 

 clearly differentiated into a basal part, which is the second valvifer 

 (fig. 24 C, D, 2Vlf), and into a large, free distal lobe, or third valvula 

 (jF/). In Gryllohlatta Walker thinks the length of the dorsal valvu- 

 lae indicates that these processes include the styli, which are distinctly 

 appendicular in the nymph; but Crampton says that the styli of the 

 ninth " coxites " are lost in the adult female, and that, with the sup- 

 pression of the styli, " the elongate coxite of the nymph becomes the 



XI A B 



-Female nymph of Magicicada scptcndecim. 



A, ventral view of end of abdomen, showing first gonapophyses {iGon) aris- 

 ing from Hmb base plates (valvifers) of eighth segment (VIIILB) behind 

 small eighth sternum {VlllStn). 



B, ninth and following segments detached from eighth segment, showing 

 second gonapophyses (^Gon) arising from bases of second gonopods (IX LB). 



dorsal valve of the adult." It is probable that small processes borne 

 on the third valvulae in tlie adult stage of some of the lower insects, as 

 in Odonata, are true styli. 



From the above evidence we may conclude that the limb bases of 

 the second gonopods in most adult female insects lose their primitive 

 styli, and that in the Pterygota each becomes secondarily differentiated 

 into a proximal second valvifer and a distal third valvula (fig. 10 C). 

 In an adult cicada the limb basis of the ninth segment is distinctly sep- 

 arated into valvifer and third valvula (fig. 31 B, 2Vlf, 3VI), but in 

 the mature nymph the outer ovipositor lobes of the ninth segment 

 are undivided (fig. ii B, IXLB), yet they are mostly occupied by 

 the imaginal third valvulae. 



The late, usually postembryonic, development of the external genital 

 processes, often after a complete and prolonged suppression of the 



