THE THORACIC APPENDAGES 



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contribution to the morphology of arthropod appendages in 

 general, but this author, unlike Snodgrass and Ewing, has not 

 concerned himself, other than incidentally, with their musculature. 

 A. Thoracic Appendages. In attempting to trace the homologies 

 of the parts of the insect leg, the best starting point is the thoracic 

 limb of a primitive Thysanuran such as Japyx or Campodea 

 (Fig. 11). The leg is seen to be a uniramous appendage and it is 



Fig. 11. Second leg of Campodea. c, coxa ; e, extensor of tibia ; et, 

 extensor of femur ; /, femur ; fc, flexor of claws ; ff, flexor of 

 femur ; ft, flexor of tarsus ; fti, flexor of tibia ; It, levator of 

 trochanter ; p, pretarsus ; r, r, rotators of coxa ; s, subcoxa; 

 t, tarsus ; ti, tibia ; tr, trochanter. (From Ewing.) 



generally agreed that it represents the protopodite and endopodite 

 of a generalised crustacean limb. Examining such an appendage 

 at its distal extremity, it will be observed that the apex of the 

 tarsus bears a somewhat complex- structure or pretarsus (trans- 

 tarsus of Hansen) which is composed of the claws and their 

 associated basal parts. The pretarsus is regarded as the 

 homologue of the dactylus which has become highly modified 

 so as no longer to show the character of a simple, claw-like 

 segment. The variations in form and structure of the claws, 

 and other parts of the pretarsus, found among insects and their 



