474 THE NERVOUS 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. 
Destruction 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 
nerve 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, 
