Nervous Systems 



819 



TABLE 78. RELATIVE PORTIONS OF BRAIN MASS OCCUPIED 

 BY DIFFERENT REGIONS (FROM HANSTROM'"} 



brain destroyed, the arthropod circuses toward the intact side. Legs on the 

 operated side tend to be flexed and low in tonus, so that the animal leans 

 toward that side. 



There are many reports that removal of the subesophageal ganglion or 

 cutting behind this ganglion stops spontaneous activity. Local segmental re- 

 flexes, however, persist. The subesophageal ganglion is apparently the prin- 

 cipal motor center, but the other thoracic and abdominal ganglia are ca- 

 pable of carrying out reflexes of locomotion, autotomv, and the like; these 

 ganglia are normally regulated by the subesophageal ganglion. 



The increased leg activity after brain removal suggests the release of the 

 ventral motor centers from inhibition by the brain. When the brain is re- 

 moved from dragon-fly larvae there is an increase in breathing frequency,^^-- 

 ^^^ whereas when the subesophageal ganglion is removed the breathing 

 frequency (determined by posterior ganglia) is decreased. Death-feigning 

 is a function of the nervous system as a whole rather than of any particular 

 ganglion; in some insects and in spiders it is relatively unaflFected by brain 

 removal; in others, as in the spider Celaenia,^^-^ there is no death-feigning 

 after brain removal. In Ranatra, the death-feigning reaction is shortened 

 after brain removal; the posterior half of the body with nerve-cord cut comes 

 out of a feint sooner than the part of the body containing the brain. -"- The 

 most convincing evidence for inhibitory action of the brain on the ventral 

 ganglia comes from electrical stimulation. Jordan-^^ stopped circus movement 

 in a crab by a weak electrical stimulation of a transected circumesophageal 

 connective. Flexion of the abdomen of Palinums and Homariis was elicited 

 by tetanic stimulation of the abdominal nerve-cord; if during this stimulation 

 the brain or circumesophageal connectives were also stimulated, the ab- 

 dominal response was diminished."*"- 



