THE HEMIPTEROUS GENUS BELOSTOMA. 65 



NERVOUS SYSTEM. 



Belostoma, when compared to most other insects, presents a considerable 

 concentration of the nervous centres. 



The cerebral ganglia are well developed, consisting of two pyriform masses of white 

 matter placed side by side, the narrow portion of which forms the commissures 

 connecting them with the cerebellum. The optic ganglia are larger than the 

 cerebral, and pass from them obliquely forwards and outwards. They are somewhat 

 clavate in form, and terminated by a rounded extremity, from which pass off the 

 optic nerves to the eye. These nerves are numerous, and are divided into two 

 bundles by a styloid process, passing vertically from the bottom of the eye to the top. 

 From the cerebral ganglia there is given off on each side, a small nerve to the 

 antennae ; a commissural filament, the nervus recwrens, to the frontal ganglion ; 

 and a commissural filament to the respiratory ganglia. 



The frontal ganglion sends off filaments anteriorly, filaments to the oesophagus, 

 and a principal branch, which proceeds backwards between the cerebrum and 

 oesophagus, to the latter of which it is finally distributed. Immediately after passing 

 the cerebrum, it has formed upon it a minute ganglionary swelling. 



The respiratory ganglia, two in number on each side, are connected with each 

 other and with the cerebrum, by exceedingly delicate commissural filaments. 



The cerebellmn or prothoracic ganglion is moderately large, and is connected to 

 the cerebrum by short, thick commissures. It sends off numerous branches^ 

 anteriorly to the oral apparatus, laterally to the anterior legs, and to the muscles 

 within the prothorax. 



The other thoracic ganglia and the abdominal ganglia are fused into a single, 

 large, cordiform mass, occupying a position at the posterior part of the mesothorax, 

 and connected anteriorly to the cerebellum by the usual double commissure, the 

 cords of which are closely applied together. It is longitudinally and transversely 

 depressed. From its antero-lateral parts it gives off a branch to the hemielytra, a 

 small branch running forward to be distributed to the muscles of the prothorax, 

 branches to the parts within the meso- and metathorax, a branch to the intermediate 

 legs, and a branch to the alse. From its postero-lateral parts, a branch to the posterior 

 legs, and a branch to the first and second abdominal segments. Posteriorly it gives 

 off five nerves on each side of the median line, which proceed backwards closely 

 united in bands, until each comes near its respective abdominal 'segment, when it 

 diverges, to be distributed to the parts within the segment, excepting the last, which 

 divides into two branches, which, with a branch from the fourth, are distributed to 



the genitalia and rectum. 



17 



