INSECTS. 285 
white, sometimes pale red or brown-yellow, and are not surrounded 
by a fibrous membrane, so that, when detached from their inser- 
tions, they may be spread out like a pencil. 
Many insects are distinguished by special art-instincts, by their 
cunning in overpowering their prey, by the care for their eges or 
young, by the construction of artificial habitations, &c. Their 
field of observation is greatly extended by the high development of 
their visual organs. The faculty of indicating beforehand changes 
of the weather by certain actions, by which some insects are dis- 
tinguished, rests probably on their finer sense of the different con- 
ditions of the atmosphere, since the air penetrates their whole body 
by the traches. In this respect, as in so many others, they resemble 
birds amongst vertebrate creatures, whose air-sacs and hollow bones 
are in connexion with the respiratory organs, and in which also 
a perfect correspondence between the external atmosphere and the 
internal parts of the body is thus maintained. 
Manifold is the damage which Insects occasion to us, as well 
by spoiling our luxuries, as by injuring or annihilating our pro- 
perty. On the other hand they procure for us many advantages, 
amongst which I need only name silk, wax and honey. But much 
more important still is the use they supply in the great economy of 
nature, and therefore indirectly to us!. The injury which they 
sometimes cause us, is not only more than counterbalanced by 
these benefits, but is for the most part only a consequence of the 
beneficent action itself. It is these small animals that nature em- 
ploys for her great purposes, and which effect by their numbers 
what the largest animals working separately are unable to perform. 
Hence they are less dependent on the will of man, which indeed 
here and there may be able to destroy a species, but is unable to 
exterminate it throughout entire districts, as it has annihilated 
different mammals in lands which they formerly inhabited. Insects 
maintain the due equilibrium in the vegetable kingdom, diminish 
putrefaction, and lastly afford to many other animals, especially 
birds, an abundant and ever present nutriment. 
The geographical distribution of Insects opens a wide field for in- 
quiry, which however has only been lately entered. Many families, 
1 On the benefit and the injury caused by Insects, see in detail Krrpy and 
SPENCE, Introduction to Entomology, 1. pp. 80—338. 
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