OF SKNSATION AND THE SENSES. 481 



head ; it was merely a continuation of the undertaking resolved upon 

 previously to the mutilation, but which, however, could only continue 

 as long as the remainder of the nervous cord still conveyed the excite- 

 ment impressed upon it by the will ; that, however, after the alteration 

 of the direction of the motion the wasp absolutely resumed its previous 

 position, I very much doubt, it is improbable in every case, and my expe- 

 riments do not tend to substantiate it. Treviranus' remark also, that the 

 Orgy la lived for three days after the loss of its head, excites just sus- 

 picion, for in all similar experiments of mine life had perfectly vanished 

 in the course of a few hours. But I am acquainted with other 

 instances in which the Noctute, after having been killed with red hot 

 needles, and extended upon the setting-board for a week, have not only 

 moved the abdomen upon the application of an excitement, but still 

 also continued to lay eggs. I think the reason of this may be found in 

 the independent irritable life of the sexual organs, which, excited by 

 the continual stimulus of the eggs contained within them, continue 

 laying them, and as long as eggs exist within them display signs of 

 irritability. To this class, consequently, the instance cited by Trevi- 

 ranus may be placed ; life no longer truly existed, but merely the re- 

 active power of the sexual organs, and they did react when excited by 

 external stimulants, but I consider the observed motion of the wings as 



O 



very doubtful ; for the needle thrust through the thorax and the other 

 red hot one would doubtlessly have had the same effect asremovmn; the 



o 



ganglion situated in the thorax ; the red heat would doubtlessly have 

 deprived it of its activity, and thereby the motion of the parts with 

 which it supplied nerves would necessarily have been destroyed. We 

 frequently observe in insects thus mutilated a still continued motion, 

 for instance, in the antennae and the parts of the mouth, when the 

 legs and wings have entirely lost theirs. 



276. 



The influence which the nervous system exercises upon the several 

 organs of the body may thus therefore be generally stated ; we have 

 still to consider more closely the nerves as the recipients of external 

 excitement, in short, as the organs of sensation in particular. It would 

 be difficult to obtain a satisfactory result upon this subject by experi- 

 ments upon insects, for, although we perceive that they are sensible to 

 external excitement, yet we cannot distinctly prove that they receive these 

 sensations through the nerves. We can maintain nothing further with 



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