INSECTS. 287 



the dissecting knife, have muscles, veins, arteries, and every other part 

 common to the larger animals ! Creatures, so very diminutive, that 

 our hands are not delicate enough to manage, nor our eyes sufficiently 

 acute to see them. 



Insects constitute the fourth class of the sub-kingdom Articulata. 

 They are characterised by their aerial respiration ; by the division of 

 the body into three very distinct regions (of which the middle one, 

 the thorax, bears three pairs of jointed legs, and usually two pairs of 

 wings) ; and by the possession of a single pair of jointed antennae. 



fig. 125. Female Crane-fly. 



The number of species is greater than is known in any other division 

 of the animal kingdom, and is only exceeded, as in fishes, by the 

 almost countless myriads of individuals which every species produces. 

 The metamorphoses which most of them undergo, before they arrive 

 at the perfect state and are able to fulfil all the ends of their existence, 

 are more curious and striking than in any other class ; and in the 

 greater number of species the same individual differs so materially at 

 its different periods of life, both in its internal as well as external con- 

 formation, in its habits, locality, and kind of food, that it becomes one 

 of the most interesting investigations of the physiologist to ascertain 

 the manner in which these changes are effected, to trace the successive 



