358 ON THE ORDERS 



may have occasion to speak, of the Winged Insects ov 

 Ptilota of Aristotle. 



These animals are the perfection of the Annulose type 

 of form ; they are in their own division what Mammalia 

 and Birds are among the Fertebrata. Their perfection 

 however must not be supposed to result from any resem- 

 blance which they bear to a Vertebrated animal, but on 

 the contrary depends on their difference from this struc- 

 ture and their greater portion of instinct. They have no 

 true circulation, at least none such has yet been detected. 

 We are even ignorant of any manner in which absorption 

 can be connected with the oscillation visible in their dor- 

 sal canal. They breathe by two principal tracheae ex- 

 tending along the whole length of the body, parallel to 

 each other, and having plexus or centres at intervals, from 

 which ramifications are dispersed throughout the body, 

 and which communicate with the external air by certain 

 orifices or stigmata. As in a Vertebrated animal the 

 distribution of the spinal and sympathetic parts of the ner- 

 vous system bears some analogy to that of the blood in 

 the veins and arteries, so the longitudinal knotted nervous 

 system of a perfect Annulose animal corresponds in form 

 to the disposition of its tracheae. 



The Winged insects appear in their perfect state to en- 

 joy all the senses of the Vertebrata, but the organs of sense 

 are entirely different in construction. Their body, which 

 is rarely composed of more than eleven segments, has three 

 very distinct divisions, termed the head, trunk, and abdo- 

 men. The head, which is always provided with two an- 

 tenna, is composed of one segment, the trunk of three, and 

 the remaining seven constitute the abdomen. 



The sexes are always distinct ; those insects which gre 



