474 ///A XKRl'OUS SYSTEM. 



and of the spinal cord and medulla oblongata, and between 

 those of the brain in Arthropods and in Vertebrates. 



In the Blow-fly imago, if the insect is decapitated, the trunk 

 exhibits reflexes, which are co-ordinate, for hours; but there 

 are no movements which can be regarded as voluntary, and 

 with the exception of the rhythmic closure of the inner valves 

 of the thoracic spiracles and quasi-respiratory, irregularly 

 rhythmic movements of the abdomen, none which can be re- 

 garded as automatic. 



It can scarcely be doubted that the so-called instinctive acts 

 of insects exhibit psychic characters, and belong to that class 

 which we ascribe to volition in Vertebrates, and that these acts 

 are controlled by the cephalic centres, which are also imme- 

 diately concerned in the senses of sight and smell. 



The sense of hearing, on the other hand, is directly depen- 

 dent on the thoracic centre, and this centre, in the Blow-fly at 

 least, is concerned in highly complex co-ordinate reflexes. This 

 is shown by the fact that a decapitated fly will clean dust or 

 water off its wings, abdomen, and tarsi by the same acts as the 

 entire insect a clear indication that the mere contact of foreign 

 matter with the integument excites reflexes, which at once dis- 

 poses of the view that insects possess little or no general or 

 tactile sensibility. 



The sudden and complete destruction of the thoracic ganglion 

 produces not only the entire cessation of movement and sensi- 

 bility in the trunk, but also of the parts of the proboscis. 

 Instruction of the thoracic ganglion of the higher insects is 

 followed by instantaneous death, just as that of the medulla 

 oblongata is in Vertebrates ; so that even those parts supplied 

 by the maxillary nerves no longer exhibit reflexes. 



In addition to the above, the following statements have been 

 more or less established from experimental evidence by the 

 various authors quoted, and, as has already been shown, some 

 inferences may fairly be drawn from the structure of the great 

 lu-rve centres. It is probable that most, if not all the following 

 statements apply to the Blow-fly imago: but the higher insects 

 are not good subjects for experiments, and at present, at least, 



