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ANATOMY AND PHYSIOLOGY OF INSECTS. 
Having thus traced the progress of insects from the 
time of their birth till they arrive at their full matu- 
rity, and likewise noticed the most remarkable fea- 
tures in their external conformation, it now becomes 
requisite to advert to their internal structure, and 
give a comprehensive view of the complex system of 
organs by which life is maintained. In these a very 
close analogy, for the most part, exists to the vital 
system of the higher animals ; but in some respects 
curious and most important differences prevail. View- 
ing the animal kingdom as forming a progressive 
series, from the most simple to the most complex 
organism, insects may be regarded as occupying 
nearly the centre of the scale ; for, though some pro- 
perties might entitle them to rank higher, there are 
others in which they are so deficient, as completely 
to counterbalance that consideration. In muscular 
vigour, for example, and the complication of the 
digestive canal, they are almost equal to the verte- 
brata, while the circulating system is so imperfect, 
that it was, till lately, a matter of doubt whether it 
deserved the name. From these considerations, it 
may be inferred that the systems of organs are neither 
very complex nor very simple, and that in these re- 
spects, there is some degree of inequality among 
them. 
