CHAPTER II 



SOME ASPECTS OF MORFUOLOGY—continued 



E. The Abdominal Appendages, p. 41 . 4. The Genitalia, p. 43. The 

 Female, p. 43 ; The Male, p. 45 ; Literature, p. 49. 



E. The Abdominal Appendages. The frequent retention of 

 abdominal appendages in insect embryos is interpreted as a 

 survival of primitive organs inherited from polypodous ancestors. 

 In the larvae of Lepidoptera, and of some other orders, certain 

 of these appendages develop into functional organs, while the 

 remainder become resorbed. In the imagines a variable number 

 of abdominal appendages are retained in the Apterygota, but 

 among the Pterygota their sole 

 survivals are represented in parts of 

 the genitalia (vide p. 43) and by the 

 cerci. 



In the Machilida?, among 

 Thysanura, the abdominal sterna are 

 more or less triangular shields, while 

 in Nicoletia each is divided into an 

 anterior and posterior s c 1 e r i t e 

 (Fig. 24). In close contact with each 

 sternum is a pair of lateral plates 

 or coxites which frequently meet along the median line. The 

 latter plates are believed to represent the basal parts of true 

 appendages whose distal parts have atrophied. They are termed 

 coxites for the reason that it is maintained they represent greatly 

 flattened coxae, but, in some cases at least, possibly other of the 

 basal segments may have become incorporated with them. In 

 Japyx and related Thysanura, the coxites are completely fused with 

 the sternum, and the entire plate thus constituted is a coxosternum. 



41 



Fig. 24. Nicoletia (Anelpistina) 

 wheeleri. Third abdominal 

 sternum s, s^ ; c, coxite ; st, 

 stylus. (From Silvestri.) 



