114 



Z<JOLOGY 



The Position of Spiders in the Zoological System. — Spiders 

 clearly belong to the arthropods because, like the grasshopper, 

 they have a thick cuticula (which is molted as the animal 

 growsj and jointed legs. Spiders differ from insects, however, 

 in several important respects. They possess four pairs of 

 legs instead of three. The head and thorax are united. The 



Fig. 11.5. — A sanrh' waste Tdune region of Fire Island Beach, Long Island) 

 where many spiders burrow in the sand. 



antennae are al)sent. Consequently it is an error to speak of 

 spiders as insects ; rather they, together with several allied 

 groups, belong to a distinct division of the arthropods, the 

 Arachnida. The Arachnida, indeed, breathe air, but the air 

 passes into a little pouch on the under side of the abdomen and 

 in between numerous thin sheets, like the leaves of a book, 

 so that the whole breathing apparatus is often called a lung 

 book. They have also a system of air-tubes which is much 



