OF INVERTEBRATE ANIMALS. 
133 
Before leaving this class of animals, I would refer to their habit of casting 
their shells. Looking at these animals bound up in their skeleton-skins, like 
coats of mail, and destined to live for many years, one would suppose they must 
possess an especial means of growth in order to render their parts adapted to each 
other. This is effected by the animal shedding every year its old skin, which it 
does at a period when a new soft matter has been deposited inside, which is in 
readiness to become hard, and takes the place of the old skin. At this time it 
makes some very violent efforts, by means of which the old skeleton in every part 
of the body is fractured and got rid of. After this exertion, the animal becomes 
exhausted, retires, perhaps for a day or two, to some quiet nook, during which 
time its new skin becomes hard, and then it resumes its former habits with in¬ 
creased dimensions. 
The next class of animals in the Invertebrate series is that of the insects ; and 
were double the time to be devoted to their consideration that has been given to 
all the other classes, it would not be more than their interesting forms, functions, 
and instincts entitle them to. Who is there that has not formed an affection 
for, or at least taken an interest in, the insect world ? From the gay plumes 
of the beauteous Butterfly that mocked our childish efforts to make it our prisoner, 
down to the common House Fly, whose extraordinary power of walking up 
window-panes and crawling over ceilings excited our youthful wonder, they are 
objects of pleasing association. From the Locust, whose myriads spread desola¬ 
tion over the earth,'"' to the little Acarus that takes possession of our flesh, and 
produces a painful disease, they are objects of fear and aversion. 
They are the most numerous and most universally-diffused of animated beings. 
Of all classes of the animal kingdom their forms are the most diversified, their 
colours are the most brilliant, and their habits the most varied. Thus constituted, 
it is not wonderful that they should have always excited the attention of 
the observer of Nature; and extensive as this class is, we are perhaps better 
acquainted with it than with any of the preceding. 
Amongst the many forms of animals that are called insects, there are two 
which have been separated from them by naturalists, and which form classes of 
their own. Insects have but six legs, but these have more than six. The first 
of these is a class to which the animals called Hundred-legs, or Centipedes, and 
Millipedes belong. They are very numerous, and there are few persons who have 
not observed them in some situation or another. Some have the power of rolling 
themselves up into a ball when touched or alarmed; and this arises from the 
segmented nature of their external covering. The same power of rolling up, 
though not so completely, is possessed in some measure by Worms and Lobsters. 
* See Naturalist, Vol. III., p. 327 _Ed. 
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