2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



Page 



V. The legs 64 



The fore legs 65 



The middle legs 66 



The hind legs 66 



The coxae and their muscles 69 



The coxo-trochanteral joint 72 



The trochantero-f emoral j oint 'j'^ 



The femoro-tibial joint 73 



The tibio-tar sal j oint 75 



The tarsal j oints 76 



The pretarsus "]"] 



VI. The abdominal petiole 80 



VII. The abdomen 84 



General structure of the abdomen 84 



The abdominal musculature 85 



The male genital organ 89 



The sting 94 



VIII. Annotated list of muscles 100 



Abbreviations used on the figures 115 



References 119 



INTRODUCTION 



An insect is preeminently a miniature machine ; its mechanical 

 elements are the skeleton and the muscles. The skeletal structure, 

 therefore, cannot be fully understood without observing its correla- 

 tion with the muscular system and the part it plays in the body 

 mechanisms. And yet, almost our entire code of insect anatomy has 

 been built up on a study of the external pattern of the skeleton, done 

 in about the same way that a casual student of geography studies a 

 map of the world. The results of our charting of the surface 

 structure, however, have not been so far wrong as might be sup- 

 posed, because all the lines that are commonly said to "divide" the 

 insect exoskeleton into sclerites have a mechanical significance, and 

 many of them are of fundamental importance in the insect mechanism. 

 The common mistake is the assumption that the sclerites themselves 

 are the fundamental elements of the skeletal organization, that the 

 sclerites have been handed down from a remote ancestor, and that 

 the primitive sclerite pattern has been somehow altered without 

 essential changes to fit the varying needs of modern insects. 



The diversifications of the insect skeleton are far too extensive to 

 be reduced to any one formula, but in general it may be said that 

 sclerites which are defined by grooves, or "sutures," in a continuously 

 sclerotized region are subdivisions of the skeleton that are merely 

 incidental to the formation of internal strengthening ridges, while 



