DEFINITION OF THE TERM INSECT. 51 



retracted within the body. This part is the principal 

 seat of the respiratory pores or spiracles, many having 

 eight in each side, while others have only one. 



Such are the principal external characters which di- 

 stinguish hisecta and Arachnida, or what we have here- 

 tofore regarded as insects, to which here may be added 

 another connected with their internal organization. The 

 union of the sexes takes place in the same manner as 

 amongst larger animals ; and the females with very few 

 exceptions, more apparent than real, are oviparous. 

 They are, however, distinguished by this remarkable pe- 

 culiarity already alluded to, that, except in the case of 

 the Arachnida, one impregnation fertilizes all the eggs 

 they are destined to produce. In most cases, after these 

 are laid, the females die immediately, and the males after 

 they have performed their office, though they will some- 

 times unite themselves to more than one female. One 

 other circumstance may be named here — that no genuine 

 insect or Arachnidan has yet been found to inhabit the 

 ocean. 



Before I conclude this letter, it is necessary to apprize 

 you, that every thing which it contains relative to the 

 characters of insects, has reference to them only in their 

 last or perfect state, not in those preparatory ones through 

 which you are aware that the majority of them must pass. 

 The peculiar characteristics of them in these states — in the 

 egg, the larva, and the pupa, will be the subjects of my 

 next letters, which will be devoted to a more detailed 

 view of the metamorphosis of insects than I gave you 

 before when adverting to this subject a . 



a See above, Vol.'. J. Ed. 4. p. 63 — - 

 E 2 



