96 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 85 



Tenthredinidae, which is numerically the tenth abdominal segment. 

 The panorpid appendages may be true cerci. Appendages occurring 

 on an apparent tenth segment might be suspected of being cerci if 

 there is evidence that this segment is composed of the tenth and 

 eleventh somites, a condition which frequently occurs in orthopteroid 

 insects, where there is no doubt that the terminal appendages are 

 the cerci. In the Tenthredinidae, however, there is reason to believe, 

 as will be shown later, that the terminal appendages of the adult are 

 not the cerci, but are appendicular organs of the tenth segment cor- 

 responding with the socii of adult Lepidoptera, and that they are de- 

 rived from the postpedes of the tenth somite of the larva. 



THE TERMINAL APPENDAGES OF ENDOPTERYGOTE LARVAE 



Appendicular organs representative of abdominal limbs are present 

 on the last abdominal segment in some or most of the larvae of 

 Neuroptera, Trichoptera, Lepidoptera, and chalastogastrous Hymen- 

 optera. These larval appendages of the terminal segment have a 

 lateral or latero-ventral position, and are movable by muscles in some 

 cases attached on their bases, but more generally inserted within 

 their distal parts. The appendages most resemble jointed limbs in 

 the Trichoptera. In Neuroptera, Lepidoptera, and Hymenoptera they 

 commonly have the structure typical of the abdominal legs of the 

 caterpillars. Since the terminal segment in these larvae is evidently 

 the true tenth somite of the abdomen, or the tenth and the eleventh 

 somites combined, there is little doubt that the terminal appendages 

 are the pygopods. The Endopterygota differ thus from the more gen- 

 eralized Exopterygota in that some of them retain the tenth segment 

 appendages in postembryonic stages. 



In addition to the true appendicular organs, there may be in endop- 

 terygote larvae also processes developed from the dorsum of the last 

 segment, and lobes of various forms associated with the anal opening, 

 or protruded from within the rectum. Processes resembling cerci 

 occur in some coleopterous larvae, but their morphology is uncertain. 



It seems probable that the pygopods of endopterygote larvae are, 

 in certain orders, caried over to the adult stage as processes which 

 sometimes occur on the proctiger, or terminal segment of the imago. 

 These processes have various forms in the Trichoptera and Lepidop- 

 tera, and are termed the socii by students of the latter ; in chalasto- 

 gastrous Hymenoptera they resemble cerci, and are frequently called 

 " cerci." Busck and Heinrich (1922) have observed that in the micro- 

 lepidoptcron Ethmia machclhosicUa the anal prolegs, with their 



