A Comparative Morphological Study of the Nervous System of the Orthoptera and Related Orders1

Abstract

The following investigation of the nervous system of Orthopteroid insects was originally planned to include both gross anatomical dissections and a finer examination of the neurohistological elements of representative species of the principal families of the order. The original purpose of the study was that it should be an introduction to the correlation of neurological structure and behaviour in invertebrate animals, that is, to establish a neurological basis for behaviour. So far only the first part of the plan has been carried out and that only in skeleton form. Histological preparations have been made but these have been used only to aid and correct the findings from gross dissection. The nervous system of insects can be conveniently divided into four anatomical divisions: (i) the "brain" proper, or supra-oesophageal (supra-stomodaeal) ganglion; (ii) the ventral ganglionic chain, composed of: (a) the suboesophageal (sub-stomodaeal) ganglion, (b) the thoracic ganglia, (c) the abdominal ganglia, (d) the ventral median nerve (sub-intestinal nervous system); (iii) the stomodaeal or stomatogastric nervous system; and (iv) the peripheral nervous system. Because it would necessitate microscopic preparations, almost exclusively, this last system will not be described. The writer wishes to express his appreciation and thanks to Professor E. M. Walker of the Department of Biology in the University of Toronto for his guiding assistance and criticism and to Professor E. H. Craigie of the same University for his help and guidance in matters of neurological technique. HISTORY Up to the present the nervous system of insects has not been the subject of much investigation. The majority of the large memoirs on the histology were published about the turn of the century. As, work was carried out with the aid of a Scholarship from the National Research Council of Canada, Ottawa. 51