NERVOUS SYSTEM. INVERTEBRATA. 37 



apart. Each gives off nerves (seen best in the right-hand 

 specimen) to the legs and body muscles, and (in the case of 

 the posterior two) to the wings. 



In the abdomen the ganglia of the chain are situated at 

 irregular intervals the first four fairly close together, the 

 last three somewhat further apart. The terminal ganglion 

 (Gth) is larger than the rest and represents a fusion of the 

 two posterior larval ganglia ; it innervates the hinder end 

 of the body, the rectum, the genital organs, and the cerci. 



Each of the other abdominal ganglia gives off a single 

 pair of nerves to the body-walls and tracheae. 



The ventral-chain ganglia are composed of definite 

 dorsal and ventral masses of neuropile, from which the 

 nerves arise by two or more independent roots, that appa- 

 rently convey either motor or sensory impulses according 

 ;is they spring from the dorsal or ventral mass. The pro- 

 bability of a localisation of motor and sensory functions in 

 opposite regions of the cord of Arthropods has been dis- 

 cussed since the idea was brought forward by Newport. 

 Later observations have tended to show that in the 

 case of Crustacea such localisation does not occur, but 

 that in Insects it most probably does. This latter con- 

 clusion rests not only upon physiological experiments, but 

 is also based upon anatomical grounds more particularly 

 upon a comparison of the alar nerve-roots in flying beetles 

 with those of beetles whose wing-cases are present but 

 immoveable. In the former case each alar nerve rises by 

 two main roots, one from the dorsal mass of neuropile, the 

 other from the ventral. In the beetles with purely pro- 

 tective non-motile wing-cases (e. g. Slaps mortisagd) the 

 dorsal root is entirely absent (Binet, I.e.). 



Preserved in Goadby solution. 



Miall & Denny, Life History and Structure of the 

 Cockroach (Periplaneta orientalis), 1886, p. 86. 



D. 29. A large female Orthopterous Insect (Karakidion australe) 

 with the nervous system shown from the dorsal aspect. 

 The thoracic ganglia are nearly equal in size, and lie, 

 widely separated, in the three thoracic segments. There 

 are six free abdominal ganglia, situated respectively in 



