PROC. EXT. SOC. WASH., VOL. 21, NO. 6, JUNE, 1919 139 



uropods, from this standpoint. The terminal abdominal limbs 

 are here referred to as "postpedes," merely for the sake of con- 

 venience in order to distinguish them from the other uropods. 



The postpedes "pp" of the larvae of Megaxyela (Fig. 51) and 

 certain other sawflies, bear a pair of postcalli "pea," or posterior 

 callus-like structures, whose function is unknown. It is possi- 

 ble that the region labeled "pea" in the larva of Pteronidea (Fig. 

 43) may correspond to the united structures "pea" of the Megaxyela 

 larva; but I am not certain of this point. The relation of the 

 appendages labeled "s" in Figs. 44 and 48, to the postpedes 

 "pp" of Figs. 43 and 51 (or to the structure "pea" of the latter 

 figures) is largely conjectural; but, since styli occur on the basal 

 segments of the limbs of such forms as Scolopendrella, Machilis, 

 etc., I hardly think that the styli "s" of larvae (Fig. 44, etc.) 

 represent entire limbs (or their vestiges), but are rather limb 

 appendages which have been retained, while the remainder of 

 the limb which bore them has become atrophied or lost. It 

 would be an extremely interesting bit of investigation to trace 

 out the relationship of the larval appendages "pp" and "pea" 

 of Fig. 51, or the appendages "s" of the larvae shown in Figs. 

 44 and 48, to the genital forceps of the adult male; but I have not 

 the necessary material, to determine which of these types of 

 larval structures form the forceps of the adult male, and must 

 therefore postpone attempting to determine this question until 

 the requisite material is available. 



It would be encroaching upon the province of the specialist 

 who has spent a lifetime in the study of a group of insects, to 

 attempt to determine the interrelationships of the different 

 members of his group, so that it is not the purpose of the present 

 paper to speculate upon the interrelationships of the forms here 

 discussed, since the study of the terminal structures alone can 

 furnish but a portion of the evidence necessary for such a study. 

 On the other hand, the study of the terminal structures can con- 

 tribute its share of the evidences of relationship which must 

 be drawn from all available sources and it may be of some in- 

 terest to briefly call attention to some of the more patent evi- 

 dences of relationship afforded by a study of the terminal struc- 

 tures. 



Rohwer and Cushman, 1917, would place the Oryssidae in a 

 distinct suborder which they call the Idiogastra, and a stud}' of 

 the terminal structures would indicate that the Oryssidae differ 

 markedly from the remainder of the sawfly group, the parts being 

 extremely highly specialized, or modified, in these forms. The 

 genitalia of a male of Oryssus sayii are not visible from the ex- 

 terior (Fig. 42), and the terminal segments are withdrawn into 



