A. D. Imms 221 



Exetastes cinctipes Retz., by Wardle (1914) in Hypamblys albopictus Grav., 

 by Cushman (1916) in Thersolochus conotracheli Riley, by Klapalek (1889) 

 in the curious larva of Agriotyjms, by Cushman (1913), and subsequently 

 by Smith (1914) in Calliephialtes, and also "by Seurat [loc. cit.) in the 

 following species: Mesochorus vittator Zett., Anilasta ebenina Grav. et 

 Thorn., Xylonomus praecatorius Fab., and Phymatodes variabile. Newport 

 (1855) similarly recognised thirteen segments in the larvae of Paniscus 

 virgatus Fourc, and AnthopJiorabia {Mellitobia) retusa Newp., while Graf 

 (1917) figures a similar number in the larva of Bassiis gibbosus Say. 

 Apparent exceptions to this rule are often difficult to explain, and very 

 possibly in some instances the small thirteenth segment has been over- 

 looked. Thus Timberlake (1912) only recognised twelve segments in the 

 larva of Limnerium validum (Cress.) and Morley (1914) mentions a 

 similar number in Paniscus cephalotes Holmgr. In Ichneumon airoj)os 

 Curt. Newport {loc. cit.) detected fourteen segments, including the anal 

 process, but the latter structure is most probably an outgrowth of the 

 thirteenth segment and this species would therefore conform in possess- 

 ing the usual number of segments. In Spilocryptus cimbicis Tschek. 

 Morley (1907) states there are twelve segments, apparently including 

 the head in his enumeration; in the onisciform larva of Mesostenus ob- 

 noxius Grav. this same observer (1906) found only nine segments. 



In the retention of ten pairs of spiracles the larva of Pimpla pomorum 

 exhibits a primitive feature not hitherto recorded, so far as I am aware, 

 in any other species of Ichneumonoidea. Laboulbene (1858) noticed nine 

 pairs of spiracles in the larva of Pimpla Fairmairii and the same number 

 has been observed by Giraud in P. detrita Holmgr., by Xambeu in P. 

 oculatoria Grav., by Ratzeberg (1844) in Ichneumon pisorius L., by 

 Berthoumieu in I. rubens Fons., and by Seurat in Pimpla mexicana, 

 Anilasta ebenina, Xylonomus jyraecatorius, Mesochorus vittator, and Phy- 

 matodes variabile. The vestigial second pair of spiracles is very small, 

 being easily passed over, and it is not improbable that, in certain cases, 

 it has been overlooked by previous observers. It is noteworthy that ten 

 pairs of spiracles are also present in the newly hatched larva of the honey 

 bee, but in this species they correspond, according to Nelson (1915), to 

 the second to eleventh segments inclusive. 



In the presence of body hairs, and the absence of either a caudate 

 appendage or anal vesicle, the larva of Pimpla pomorum exhibits features 

 that are characteristic of Ichneumons leading an ectoparasitic mode of 

 Hfe. 



