28 ILLINOIS BIOLOGICAL MONOGRAPHS (346 



on the caudal margin of the tergum dorsad of the membranous suranal 

 lobe. These processes are always two in number and more or less constant 

 in position in nematid larvae, but vary in size and shape altho constant 

 within species. They are conical, subconical, sharply or bluntly pointed, 

 truncate, or distinctly swollen at the distal end as in Pteronidea trilineata. 

 The tenth abdominal tergum of the spinous larvae of the Blennocampinae 

 is provided with several symmetrically arranged conspicuous spinous 

 processes on the caudal portion and in part along the caudal margin. The 

 larva of Dimorphopteryx is unique among the Emphytinae in the possession 

 of four very distinct, sharply pointed spinous protuberances along the 

 caudal margin of the ultimate segment dorsad of the suranal lobe. In 

 certain of the gall-making species of Pontania the caudal end of the tenth 

 abdominal tergum is produced caudad and forms a median prominence 

 which usually has two minute strongly chitinized points close together on 

 the meson. A similar protuberance is found in the larvae of Caulocampus 

 acericaulis. In the Siricidae a pair of minute sharply pointed solid chitin- 

 ized spines occurs on the tergum of the ultimate segment, one on each 

 side of the median longitudinal depression (Fig. 113). 



These protuberances have been variously designated. Crampton 

 (1919) considers the paired protuberances and spines to be homologous 

 with the cerci of Orthoptera and Ephemeridae. If they represent rudi- 

 mentary cerci they must belong to the eleventh abdominal segment, 

 the telson of embryologists, since the true appendages of the tenth segment 

 are transformed into the anal larvapods. But this homology is open to 

 question because these protuberances are mere projections of the surface 

 and not at all appendages in a morphological sense, and, furthermore, 

 because in other larvae the number and position of the protuberances vary 

 considerably. No one would suggest that the caudal tubercles and spinous 

 processes of Dimorphopteryx, Blennocampa, Hypergyricus, Caulocampus, 

 and others are homologous with the cerci of generalized insects; yet, there 

 is no reason to assume that the caudal tubercles of these larvae are differ- 

 ent in origin, structure, and function — whatever that may be — from the 

 suranal paired processes of the nematid larvae. These protuberances 

 may or may not be at all related genetically to the suranal median process 

 of the Cephidae and its allies. At any rate our present knowledge does 

 not permit any definite conclusion regarding the true nature or homology 

 of these structures. The interpretation advanced by Middleton (1921) 

 seems more reasonable. He named these protuberances pseudocerci. 



Subanal Appendages. — The larvae of the Pamphiliidae (Figs. 91, 95) 

 and Cephidae (Figs. 108, 109, 111, 116, 117, 118, 119) possess a pair of 

 subanal appendages on the ultimate segment, one on each side ventrad 

 of the lateral ends of the anal slit. These appendages are long, setaceous, 

 and three-segmented in the Pamphiliidae, but are rudimentary, papilliform, 



