DEFINITION OF THE TERM INSECT. 15 



with the details of the animal kingdom at large to hazard 

 any decided opinion upon Mr. MacLeay's whole system, 

 or to ascertain whether all these classes are sufficiently 

 distinct 3 . My sentiments with regard to those of the 

 Annulosa I shall state to you hereafter. 



Upon a future occasion I shall consider more at large 

 the station to which insects seem entitled in a system of 

 invertebrate animals, which will not accord exactly with 

 that assigned by MM. Cuvier and Lamarck. But I am 

 now in a field in which I have no intention to expatiate 

 further, than as it is connected with the subject of the 

 present letter. I shall therefore confine myself in what 

 I have more to say to the definitions of Insecta that have 

 been given by modern authors, beginning with that of 

 the zoologist last mentioned. Insects form a part of his 

 second group, which he terms sensitive animals [animaux 



sensibles), which group he thus defines : " They are sen- 

 tient, but obtain from their sensations only perceptions 

 of objects — a kind of simple ideas which they cannot 

 combine to obtain complex ones. Charact. No vertebral 

 column ; a brain, and most commonly an elongated me- 

 dullary mass ; some distinct senses; the organs of move- 

 ment attached tinder the skin : form symmetrical, by 

 parts, inpairs b ." This division of animals, from the 



1 The number Jive, which Mr. MacLeay assumes for one basis of 

 his system as consecrated in Nature, seems to me to yield to the 

 number seven, which is consecrated both in Nature and Scripture. 

 Metaphysicians reckon seven principal operations of the mind ; mu- 

 sicians seven principal musical tones; and opticians seven primary 

 colours. In Scripture the abstract idea of this number is — comple- 

 tion-r-fullness — perfection. I have a notion, but not yet sufficiently 

 matured, that Mr. MacLeay's quinaries are resolvable into septenaries. 



b Anim.sans Vertebr.'i. 381. 



