1584 Insects. 



ferent sensations daily affecting us, and each in its own place neces- 

 sary for our safety and existence. Let us now reflect which of them 

 are most necessary to that of an insect, and whose presence is most 

 compatible with what we know of the structure of its parts. An in- 

 sect, enclosed in a horny case, does not need, and indeed could not 

 possess, that perception of pricking which exists in the higher soft- 

 skinned animals : such a sensation does not exist invariably even in 

 the human species, as the exit of many needles from various parts of 

 the body of a lady who had swallowed them, causing no pain until 

 they approached the surface, abundantly testifies. And further, is it 

 probable that an insect would be endowed with a sensation, rendering 

 it liable to a pain which for purposes of protection would be useless ? 

 Consider its internal structure ; there is no single central heart driving 

 the blood in closed vessels through insulated lungs, as the blood, after 

 being driven towards the head by the lengthened and many-parted 

 dorsal vessel, finds its way back through capacious venous sinuses, 

 which scarcely confine it, so that even the alimentary canal and se- 

 cerning organs float loosely in the ambient fluid ; and as the system 

 of respiratory organs is distributed in multiplied ramifications through- 

 out the entire body, there is not the slightest danger of that suffocation 

 which in higher animals must result from internal thoracic hceniorrhage ; 

 also from the constitution of the main trunk of the nervous system, of 

 two thin filaments connecting ganglia, which are protected by inward 

 processes of the envelope, but little danger can accrue to it. May we 

 not thus account for that total absence of injury from an impaling 

 pin, which so many experiments have testified ? And again, I ask, is 

 it probable that such a sensation as that of pricking would be imparted 

 to protect from an injury existing only in those imaginations of our 

 own, which I have at first suggested the propriety of shaking off? 

 But the insect must experience the feeling of resistance, or it cannot 

 know when it has the power of moving on its legs : this feeling is 

 probably most acute in the antennae, which it so frequently moves 

 about, to ascertain the presence of near objects ; and perhaps in those 

 where the antenna has at its end a soft substance, there may be also 

 a perception analogous to that delicate one existing in our finger- 

 ends. An extreme of heat or cold may cause an insect's death . this 

 sensation, confined to no part of the body, may also here exist, and 

 warn it of such a danger, thus causing the terrible anxiety manifested 

 when escape is rendered impossible. I have occasionally witnessed 

 this phenomenon, but never reflected on its probable cause, until the 

 enquiry suggested by Mr. Guyoifs experiments (which 1 am happy to 



