PHYLUM ARTHROPODA — CLASS ARACHNIDA 



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as feelers, and in the males the terminal segments are used as copu- 

 latory organs. These palpal organs are useful in the classification 

 of many of the families of spiders. The basal segments, or maxillae, 

 are used in chewing the food. The four following pairs of appendages 

 are the legs. Each leg is made up of seven segments; namely, the 

 coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus. 



The eyes are located on the front of the head and usually are eight 

 in number ; some species have fewer, but never more than this number. 



The cephalothorax and abdomen are connected by a narrow waist. 

 On the under side of the abdomen, just back of the last pair of legs, 



Fig. 167. — Ventral view of adult female, black widow spider, Latrodectus 

 mactans, hanging from web. The hour glass on the ventral part of the abdomen is 

 clearly shown. (From Knowlton, by permission of the Utah Agricultural Experi- 

 ment Station.) 



are the front pair of breathing openings or slits which communicate 

 with the lung books. Near these is the opening of the reproductive 

 organs, which in the females is protected by a plate called the 

 epigynum. Near the end of the abdomen are three pairs of spin- 

 nerets. In front of these is an opening to the tracheae and just pos- 

 terior to them is the anus. 



The digestive system of the spiders is well adapted for its fluid food. 

 The mouth is located just behind the chelicerae. Through its small 

 opening the liquid portion of the prey is sucked up by means of 

 muscles which are attached to the dorsal wall of the cephalothorax 



