THE THORACIC MECHANISM OF A GRASSHOPPER. 

 AND ITS ANTECEDENTS 



By R. E. SNODGRASS 



Bureau of Entomology 



U. S. Department of Agriculture 



CONTENTS 



PAGE 



Introductioi: i 



I. General discussion 3 



The thoracic terga 5 



The thoracic pleura 10 



The thoracic sterna 21 



II. The thoracic skeleton of Dissosleira 33 



The cervical sclerites 33 



The prothorax 34 



The pterothorax 37 



III. The thoracic muscles of Dissosteira 51 



Muscles of the neck and prothorax 53 



Muscles of the pterothorax 59 



The mesothoracic muscles 60 



The metathoracic muscles 66 



IV. The legs and their muscles 72 



Structure of the legs 73 



Aluscles of the legs 78 



V. The wings and their mechanism 84 



Structure of the wings 84 



The wing mechanism 92 



VI. The spiracles 99 



Abbreviations used on the figures 108 



References lOQ 



INTRODUCTION 



The principal elements in the motor mechanisms of arthropods are 

 the muscles and the hody wall, though the blood often plays an im- 

 portant secondary part as a hydraulic medium. All movements, how- 

 ever, come primarily from muscle contractions. A contracted muscle, 

 when it relaxes, must be actively extended before it can operate again, 

 and therefore muscles generally occur in antagonistic sets. But the 

 muscles of insects are not necessarily opposed by other muscles ; the 

 counter force may he produced by the elasticity of the part of the 

 body wall on which a muscle is attached. For this reason it is often 



Smithsonian Miscellaneous Collections, Vol. 82. No. 2. 



