BOOK VV. FOINTED ANIMALS 
Ci sar LER 
THE CRAB AND SCORPION GROUPS 
BY W. F. KIRBY, F.L.S. 
HIS section of animals is often called a‘ sub-kingdom,” 
and differs from back-boned animals in having the frame- 
work of the body outside. That is, instead of a skeleton, 
Crabs, Spiders, Centipedes, and Insects are protected either by a 
hard shelly casing, or by a tough skin, to which the muscles are 
attached; and this arrangement renders them much stronger and 
much less susceptible to injury, in proportion to their size, than 
vertebrate animals. They have cold blood, generally of a white 
colour; and their bodies and limbs are usually composed of a 
considerable number of separate joints. 
The group is a very large one, and it is probable that there 
are at least 300,000 different 
kinds of insects already known, 
while the total number of spe- 
cies now existing is estimated 
by different entomologists as 
from two to ten millions. It 
is, therefore, no exaggeration 
to say that every word of our 
= = 4 
{ X, brief account of the Insects 
l | represents from ten to twenty 
Fike SOmae ~~ known species at least. The | 
BARNACLES other classes of the group are 
A species which commonly attaches also very numerous. Our ac- 
itself to ships bottoms and S i 
‘Faaling aweerkage count must necessarily be very 
short; the characters of the 
principal classes of the Jointed Animals are referred to in 
their places, 
CRABS, LOBSTERS, SHRIMPS, WOOD-LICE, BARNACLES, ETC, 
Jointed animals are generally provided with one pair 
of long jointed organs, called ‘“ antennz,” a naturalised 
word derived from the Latin, in which language antenna 
means a sail-yard. They are often called “ feelers,” and 
usually fulfil this function at least; but they are also ku 
frequently organs of smell, and sometimes probably of BIR, Fy The ARG Repenale Dew 
hearing and other senses. One peculiarity of the CRAB A PAIR OF BARNACLES 
and LOBSTER group is that they are generally furnished : 
; , ’ ‘ The larger sexe of this photograph exhibits more 
with two pairs instead of one pair of these organs. structural details than the last 
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