46 



ZOOLOGY 



jaws (gnathites). Then come the Arachnida, in which the 

 first pair of limbs is a small pair of claws termed chelicerse, 

 and this is the only pair which is in front of the mouth ; the 

 following pairs of limbs may have their bases slightly broadened 

 and roughened so as to assist in chewing, but they are also 



used for walking. Most 

 Arachnida are terres- 

 trial, but there are some 

 most interesting aquatic 

 forms. Finally, we have 

 to consider the Insecta, 

 in which there is also only 

 one pair of limbs in front 

 of the mouth, but this 

 pair are converted into 

 feelers or antennae. Three 

 pairs of limbs are con- 

 verted into jaws, and the 

 region of the body to 

 which jaws and feelers 

 are attached is termed the 

 head, and is separated 

 from the rest by a thin 

 flexible region called the 

 neck. Behind the neck 

 comes a region to which 

 three pairs of long limbs 

 Fia. 18. A scorpion as an example of used for walking are 

 Arachnida viewed from below ; ch, attached : this is the 

 chelicerss; g, chewing processes 



thorax, and it consists 



borne at the bases of I, the walking /. ,, .^ Q ^4. a TU^ 



legs ;o, mouth. > of three segments. The 



last two of these ID 

 many cases bear flat 



outgrowths used for flying, which are termed " wings." 

 Following the thorax comes a region consisting of nine or 

 ten segments devoid of appendages, which is termed the 

 abdomen. The word " insect," which literally means "cut 

 into," refers to the striking differentiation of the body into 

 these three regions. The Insecta breathe by means of air 

 tubes which ramify through their bodies, and they are typically 



