26 



SOME ASPECTS OF MORPHOLOGY 



their individuality in such a highly evolved class as the insects, 

 especially in view of the fact that they are only developed as 

 separate sclerites among some of the more generalised Mala- 

 costraca. 



On turning to the Chilopoda it will be noted that two segments 

 similarly intervene between the coxa and femur — these are the 

 trochanter and prsefemur of Hansen or the first and second 



F F ^ ,5 



Fig. 13. Structure and musculature of the coxa, trochanter and 

 base of femur. A, diagram of typical musculature of coxa, 

 trochanter, and base of femur ; B, trochanter and base of femur 

 of an ichneumonid (Megarhyssa), showing basal subdivision 

 (F^) of the femur (F) ; C, trochanter and base of femur of 

 middle leg of dragon-fly nymph (Aeschnidae), showing double 

 structure of the trochanter (iTr, 2Tr). Be, basicosta of coxa ; 

 be, basicostal suture ; Bex, basicoxite ; Cx, coxa ; F, femur ; 

 F^, basal subdivision of femur ; /, posterior coxo-trochanteral 

 articulation ; g, basicosta of trochanter ; h, ridge between 

 subdivisions of trochanter ; i, basicosta of femur ; j, femoral 

 ridge setting off basal subdivision of femur ; O, levator muscle of 

 trochanter ; P, thoracic branch of depressor of trochanter ; 

 Q, coxal branch of depressor of trochanter ; R, reductor muscle 

 of femur ; *S', levator of tibia ; T, depressor of tibia ; Tr, tro- 

 chanter ; ITr, 2Tr, first and second subdivisions of trochanter. 

 (After Snodgrass.) 



trochanters of other authors. The possibility that these parts 

 are homologous with the divided trochanters of the Odonata 

 should not be overlooked, and in Lithobius the first trochanter is 

 greatly reduced, as in the Insecta. 



In many of the parasitic Hymenoptera it is well known that the 

 trochanter appears to consist of two segments, but comparative 

 study over a series of genera reveals the fact that the second 

 segment is merely the separately differentiated proximal end of the 



