BOOK V. JOINTED ANIMALS. 



CHAPTER I. 



THE CRAB AND SCORPION GROUPS. 



BY W. F. KIRBY, F.L.S. 



THIS section of animals is often called a " sub-kingdom," and 

 differs from back-boned animals in having the framework 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 species 

 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 



Photo by E. Connold. 



BARNACLES. 



! represents from ten to twenty 

 J known species at least. The 

 other classes of the group are 

 also very numerous. Our 

 ^t 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 "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. 



670 



Photo by W. P. Dando, F.Z.S., Regent's Par 

 A PAIR OP BARNACLES. 



The larger size of this photograph exhibits 

 structural details than the last. 



