PROC. ENT. SOC. WASH., VOL. 23, NO. 6, JUNE, 1921 141 



abdominal structures of sawflies, applies the term "cerci" to a 

 larval and an adult appendage. In a paper recently submitted 1 

 the author indicated the existence of a homology between the 

 larval postpedes and the adult cerci, thus disposing of the term 

 cerci, as applied to larval structures other than the postpedes 

 and leaving those protuberances of the larva designated as 

 "cerci" by Crampton without a name. In the following para- 

 graphs the writer, (1) treats somewhat more in detail his 

 reasons for believing the larval postpedes and adult cerci to be 

 homologous; (2) compares the styli, or arthrostyli, of the 

 Pamphiliinae and Cephidae with the postpedes of other sawfly 

 larvae and advances some reasons for considering them homolo- 

 gous; (3) suggests a new term for those larval structures desig- 

 nated "cerci," by Crampton; and (4) discusses briefly the cerci 

 of the adult male Tremex. 



Postpedes and Cerci. 



The conclusion that the postpedes are homologues of the cerci 

 was reached by means of a study of the ontogenetic development 

 of Pteronidea ribesii supplemented by the position that the cerci 

 occupy in relation to other parts of the adult. 



In the formation of the pupa there are below the anus, and at 

 the laterad caudad extremities of the venter of the tenth urite, 

 a pair of rounded protuberances. (See Plate XI, Fig. I.) These 

 lobes are formed from that area of the larva which gives rise to 

 the postpedes and are the pads within which the adult cerci are 

 developed, therefore they are undoubtedly homologous with 

 these appendages (Plate XI, Figs. H and J). In the adult, the 

 cerci do not spring from the chitin of the tergum, but are sepa- 

 rated from that sclerite by a narrow strip of the membrane which 

 constitutes the venter of the tenth urite. They are also below 

 the anus and in one abnormal, adult, female of Pteronidea 

 ribesii the cerci were fused together forming a single structure 

 projecting below the anus. Thus, it would seem to the author 

 that the cerci of the adult are not homologous with the so-called 

 "cerci" of the larvae and that they are developed from the post- 

 pedes. 



Postpedes and Styli. 



The tenth, or terminal, abdominal segment has, in a number of 

 sawflies, a pair of uropods or postpedes and in some of those 

 sawflies (Cephidae and Pamphiliinae) not possessing what have 

 been recognized as postpedes, there are a pair of laterad appen- 

 dages on the sternum of this segment to which the term styli or 

 arthrostyli, has been applied (Plate XI, Figs. A and G). Since 

 these styli bear a very close structural resemblance to, and 

 occupy a position similar to, the thoracic legs (in the Pam- 



To the Proc. Ent. Soc. Wash. 



