BOOK V, 
JOINTED ANIMALS 
CHAPTER I 
THE CRAB AND SCORPION GROUPS 
BY W. F. KIRBY, F.L.S. 
T 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 
brief account of the Insects 
represents from ten to twenty 
known species at least. The 
other classes of the group are 
also very numerous. Our ac- 
count must necessarily be very 
short ; the characters of the 
principal classes of the Jointed Animals are referred to in 
their places. 
Photo by E. Connold 
BARNACLES 
A species ^vh'ich commonly attache, 
itself to ships' bottoms and 
floating wreckage 
Crabs, Lobsters, Shrimps, Wood-lice, Barnacles, etc. 
Jointed animals are generally provided with one pair 
of long jointed organs, called “ antennae,” 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 
frequently organs of smell, and sometimes probably of 
hearing and other senses. One peculiarity of the Crab 
and Lobster group is that they are generally furnished 
with two pairs instead of one pair of these organs. 
272 
Photo by IV, P, Dandoy F.Z.S,.^ RegenPs Park 
A PAIR OF BARNACLES 
The larger size of this photograph exhibits more 
structural details than the last 
