TEXT-BOOK OF ENTOMOLOGY 



abdomen being each a distinct motor and respiratory centre. The 

 two halves of a ganglion are independent of each other. 



According to Faivre, the brain is the seat of the will and of the 

 power of coordinating the movements of the body, while the 

 infraoesophageal ganglion is the seat of the motive power and also 

 of the will. 



The physiological experiments of Binet, which are in the line of 

 those of Faivre, but more thorough, demonstrate that an insect may 

 live for months without a brain, if the subresophageal ganglion is 

 left intact, just as a vertebrate may exist without its cerebrum. As 

 Kenyon says : " Faivre long ago showed that the suboesophageal 

 ganglion is the seat of the power of coordination of the muscular 

 movements of the body. Binet has shown that the brain is the 

 seat of the power directing these movements. 'A debrained hexa- 

 pod will eat when food is placed beneath its palpi, but it cannot go 

 to its food even though the latter be but a very small space removed 

 from its course or position. Whether the insect would be able to 

 do so if the mushroom bodies only were destroyed, and the antennal 

 lobes, optic lobes, and the rest of the brain were left intact, is a 

 question that yet remains to be answered ' ' (Kenyon). 



In insects which are beheaded, however readily they respond to 

 stimulation of the nerves, they are almost completely wanting in 

 will power. Yet insects which have been decapitated can still walk 

 and fly. Hymenoptera will live one or two days after decapitation, 

 beetles from one to three days, and moths (Agrotis) will show signs 

 of life five days after the loss of their head. 



That the loss of will power is gradual was proved by decapitating 

 Polistes pallipes. A day after the operation she was standing on her 

 legs and opening and closing her wings ; 41 hours after the operation 

 she was still alive, moving her legs, and thrusting out her sting when 

 irritated. Ichneumon ott'osus, after the removal of its head, remained 

 very lively, and cleaned its wings and legs, the power of coordination 

 in its wings and legs remaining. A horse-fly, a day after decapita- 

 tion, was lively and flew about in a natural manner. 1 



When the abdomen is cut off, respiration in that region is not at 

 first interrupted. The seat of respiratory movements was referred 

 by Faivre to the hinder thoracic ganglion, but Plateau says that this 

 view must be entirely abandoned, remarking: "All carefully per- 

 formed experiments on the nervous system of Arthropoda have 

 shown that each ganglion of the ventral chain is a motor centre, and 



1 A. S. Packard, Experiments on the vitality of insects, Psyche, ii, 17, 1S77 



