THE CERVICOTHORACIC NERVOUS SYSTEM 

 OF A GRASSHOPPERS 



By JOHN B. SCHMITT 



Rutgers, The State University, New Brnuszmck, N. J. 



INTRODUCTION 



The nervous system of insects has long been a subject for inten- 

 sive study. The ventral nerve cord and the changes exhibited by it 

 have been described in many forms, at least in its gross aspects, and 

 in more recent years the histology and physiology of the nerves and 

 ganglia have been attacked by many workers. Yet the literature con- 

 tains relatively few detailed studies of the segmental nerve patterns 

 of insects with respect to the muscle groups innervated. Most text- 

 books dismiss the subject with only a brief statement to the effect that 

 the muscles of a segment are innervated by lateral nerves from the 

 ganglion of that segment. This paper is, in part, an attempt to supply 

 some information on the arrangement of the nerves with respect to 

 the musculature in the cervix and thorax of a grasshopper, Dissosteira 

 Carolina. A previous paper by the writer (1954) described the pat- 

 tern of nerves and muscles in the pregenital abdominal segments of 

 the same insect and of certain other Orthoptera. 



Various workers have made detailed studies of muscle-nerve pat- 

 terns in insects, but attempts to compare such innervation patterns in 

 order to discover segmental features common to several orders have 

 generally been futile, largely because of difficulties in recognizing 

 homologous nerve groups. The concept of an underlying homology 

 of musculature, on the contrary, has been explored to the point of 

 supplying important evidence on the evolution of the insect thorax 

 and appendages. If there was a common ancestral pattern of seg- 

 mental musculature, an accompanying ground plan of nerves to those 

 muscles seems to be implicit in the concept. 



If the innervation pattern as well as the musculature was homolo- 

 gous in each segment of this ancestor, the particular nerve configura- 

 tions exhibited now in any segment are simply modifications of that 

 original pattern. Since the essential purpose of a nerve is to conduct 

 nerve impulses, there would appear to be less occasion for selective 



1 Paper of the Journal Series, New Jersey Agricultural Experiment Station, 

 Rutgers, The State University of New Jersey, Department of Entomology. 



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