16 ON THE ANATOMY OF THE FLY. 



glion. This is the nerve centre of animal life ; its nerves are 

 both motor and sensitive ; it gives off likewise two pairs of nerves, 

 which are supplied to organs of special sense ; and its destruction 

 results in the instantaneous death of the insect. If a pair of 

 forceps are dexterously used so as to crush the whole thoracic 

 ganglion at once, not a single movement will follow its destruc- 

 tion, except it be the slightest possible quivering of the 

 muscles. 



On the other hand, the removal of the insect's head, and with it 

 of course, the whole cephalic ganglion, does not destroy the life 

 of the trunk and limbs, but reflex movements can be produced 

 for hours after by touching any part of the integument, but 

 especially the integument of the abdomen. 



When the head is removed frotm the fly there is nothing more 

 striking than the different character of the phenomena exhibited 

 by the parts. In the head a convulsive movementof the tongue 

 and antennae follows the division of the nervous cord which 

 unites the two nerve centres ; this continues at most a few 

 seconds, but no reflex act follows the application of external 

 stimulus afterwards. Of course we cannot tell to what extent the 

 functions of the cephalic ganglionremain, but their duration is pro- 

 bably short. Perhaps they cease as soon as the nerve of communi- 

 cation between the head and thorax is severed. On the 

 other hand, although the trunk continues to manifest signs 

 of life for many hours, no movements, except those which 

 result from the stimulus or shock produced by dividing the 

 great cephalo-thoracic nerve trunk at the moment of division, 

 take place, except the respiratory movement of the abdomen, 

 till some external stimulus is applied. A breath of air, or a 

 touch with a needle point in any part of the integument, will 

 produce vigorous movement of the legs and wings for hours 

 after decapitation, resulting either in an attempt to run or fly, 

 and a little water or dust placed upon the posterior tarsi or 



