NO. 8 INSECT ABDOMEN SNODGRASS IO9 



The proctiger of the lower Hymenoptera is of particular interest 

 because of the pair of appendicular processes arising from it. In 

 Pteronideathe proctiger consists of a bonnetlike dorsal plate (fig. 35 B, 

 Ptgr) and of a broad, flat, membranous ventral flap, which enclose 

 the anus (An) between their distal ends. The appendicular processes 

 (Soc) are attached to the margin of the lower ends of the dorsal plate 

 of the proctiger. The writer has been unable to find any trace of 

 muscles connected with these appendages, though a large muscle ex- 

 tends into the proctiger from the ninth segment dorsal to the base of 

 each process. 



The proctiger of the Hymenoptera is probably a compound segment 

 containing the tenth and eleventh abdominal somites, though there is 

 little evidence even in the larvae of the presence of the eleventh somite. 

 It has been shown by Nelson (1918), however, that in the embryo and 

 young larva of the honey bee there is evidence of 1 1 abdominal ganglia. 

 The newly hatched larva has nine distinct ganglionic masses in the 

 nerve cord of the abdomen, the last of which lies in the caudal region 

 behind the eighth segment, and contains three pairs of nerve centers, 

 making thus a total of 11 pairs of gangHonic centers in the abdomen, 

 which is indicative of the presence of the same number of somites. 

 In the mature larva the composite end ganglion has united with the 

 ganglion of the eighth somite to form the definitive terminal ganglion 

 of the adult. 



The appendages of the proctiger have usually been regarded as the 

 cerci. If, however, we accept the embryological evidence that cerci are 

 the appendages of the eleventh abdominal segment, it is difficult to see 

 how these appendicular processes of the proctiger in adult Hymen- 

 optera can be cerci, since in larval stages of the same insects the 

 eleventh segment is absent, or represented only by the circumanal lobes 

 of the terminal segment. The postpedes, or terminal appendages, of 

 sawfly larvae clearly belong to the tenth abdominal segment, as do 

 those of lepidopterous larvae, and it is claimed by Middleton (1921) 

 that these larval appendages of Pteronidea ribesii give rise to pro- 

 tuberances of the tenth segment in the pupa within which the pro- 

 cesses of the proctiger of the adult are developed. Though Middleton 

 calls the adult processes " cerci " his own evidence suggests that they 

 are identical in origin with the appendages of the tenth segment of 

 the larva and are, therefore, not true cerci. The same argument ap- 

 plies to the appendicular processes of the proctiger present in adult 

 males of some Lepidoptera, termed the socii by lepidopterists. The 

 socii evidently are not cerci, since the eleventh abdominal segment is 

 suppressed in the caterpillars and the last appendages in both the 



