THE THORACIC APPENDAGES 27 



femur. In many cases the separation is complete, but in numerous 

 other instances the so-called second trochanter is only demarcated 

 from the rest of the femur by a weak suture or a slight constriction 

 (Fig. 14). This conclusion is borne out by the relations of the 

 reductor femoris muscle which is inserted on an inflexion from the 

 base of the second segment of the trochanter : furthermore, the 

 depressor muscle of the tibia passes through this segment and is 

 attached anteriorly close to the insertion of the muscle just 

 mentioned (Fig. 13, B). 



The homologies of the coxa now require consideration. Snodgrass 

 believes that the insect coxa is the homologue of the part bearing 

 the same name in Crustacea and that the first trochanter of the 



Fig. 14. Basal segments of fore leg of a Cynipid, Rhoptromeris eucera, 

 female, showing rudimentary second trochanter (<i). c, coxa ; 

 t, true trochanter ; /, base of femur. 



Odonata represents the basis which is otherwise wanting among 

 insects. Hansen sees in the insectan coxa the counterpart of the 

 basis, while the trochanter he believes corresponds with the true 

 or primitive coxa of the biramous limb. The term subcoxa is 

 not employed by Hansen, who uses the name pretrochantin 

 (precoxa) for the sclerite in question. A great difficulty in this 

 connection is the complex and extremely variable condition 

 presented by the small basal leg-«clerites in different insects. 

 The subject is discussed by Snodgrass (1927, 1935), who maintains 

 that in the primitive insect leg a single proximal sclerite the 

 subcoxa (praecoxa of Hansen) intervened between the coxa and the 

 thoracic wall. Further discussion of this subject is given in the 

 next section dealing with the pleura. All that need be stressed 

 here is that while the homologies of the four distal segments of 



