3 



the activity of certain animalculae which exhibit no nerv- 

 ous fasciculi ; and it is in reference to this supposed fact 

 that an ingenious dentist of this city (M. Regnard) has 

 advanced an opinion, that tooth-ache does not require a 

 seat in the nerve, but that it is competent to the bony 

 matter of the tooth itself to incur this penalty. As 

 sensibility however, is incontestably united to a nervous 

 structure through all the races of being in which 

 sensibility is most conspicuous, or can best be traced 

 and verified, we would make light of the exception, 

 if indeed it be such, and hold it more useful to en- 

 quire rather into the character and extent of such a nerv- 

 ous arrangement as insects really exhibit. 



The nervous system then in insects, to confer so large 

 a title on a medullary cord which runs through the animal, 

 and gives off a few branches to the organs which it visits, 

 is of the simplest character ; it is composed of two sub- 

 stances, an external of darker colour, and an internal of 

 whiter matter, called, from some resemblance to that of 

 the human brain, cortical and cineritious. In examining 

 the nervous rope more closely, it is found to consist of 

 two easily discernible elementary threads, more intimately 

 united at particular points than at others, and that union 

 effected by roundish knobs or ganglions, which appear 

 as so many small inequalities or excrescences, occurring 

 at unequal intervals, in uncertain number, and of irre- 

 gular size. As to external manifestations of an inter- 

 nal nervous centre, in the existence of organs of the par- 

 ticular senses ; it is observable that eyes, which constitute 

 the most remarkable of such organs, are in insects 

 not universal ; but as insect eyes have optic nerves, and 

 as the optic nerves in man proceed from the brain, the 

 first ganglion, from which they proceed in insects, passes 

 with some physiologists for an unequivocal brain ; others 

 being disposed to look on all the ganglia as so many 

 equal brains ; while a third school, consider the supposi- 



