132 
Psyche 
[September 
attached to pleuron and as heavily sclerotized as the other structures. 
Sternum joined only internally to pleuron, does not extend in front 
of the coxa. Anterior and posterior collars absent, coxal articulation 
external so that considerable cervical, intersegmental, and pericoxal 
membrane is exposed (fig. 23). 
This configuration is most similar to the extant Australian genus 
Ithone (Neuroptera) (fig. 20) but with a large, articulatory tro- 
chantin, as in the Trichoptera (fig. 22). Reducing the trochantin 
while maintaining associated musculature may be a modification for 
increasing the angle of coxal flexation. Division of the pleuron into 
Eps _ _ 
CS_ __ 
Tn 
Figs. 20-22. Prothoracic structure of the Lower Holometabola. 
Fig. 20. External lateral view of Ithone sp. (Neuroptera). 
Fig. 21. Internal lateral view of Panorpa virginica (Mecoptera). 
Fig. 22. External lateral view of coxal articulation of Ptilostomis ocel - 
Yifera (Trichoptera). 
