THE PLACE OF SPIDERS IN NATURE 23 



distal end, and a shorter, movable fang, which lies in the groove 

 when at rest. The sharp fang is the part that is thrust into the prey. 

 Near its end is a tiny opening through which venom flows into the 

 wound. The poison glands, present in all but two small groups of 

 spiders, are associated with the chelicerae, sometimes being entirely 

 contained within the basal segment, but in most true spiders extend- 

 ing farther back into the head as more or less voluminous pouches. 



All spiders are predaceous, subsist on the body juices of living 

 animals, and only rarely can be duped to accept dead food. The 

 bulk of their food is made up of insects, which are subdued by 

 their venom. Their method of feeding is a most unusual one. The 

 sharp edges of the maxillae and the chelicerae are used to crush and 

 break the fresh body of the prey, which at the same time is bathed 

 with quantities of digestive fluid from the maxillary glands. The 

 softer parts of the animal are broken down and predigested to a 

 liquid state, and this liquid is sucked into the stomach by means of 

 powerful muscles. As the prey is rolled and chewed, it gradually 

 becomes smaller and smaller until only a little ball of indigestible 

 matter remains. This is finally cast aside, or, in some instances, is 

 hung up on the egg sac or in some section of the web, a trophy 

 of the chase. In some hard-bodied insects the juices are sucked 

 through holes made by the chelicerae, and the shell of the drained 

 insect is then discarded. Some spiders require several hours of nearly 

 continuous effort to digest completely an ordinary fly. It is doubt- 

 ful that spiders ever actually imbibe solid food material through the 

 small mouth, and probable that even small snakes, birds, and mam- 

 mal prey are first reduced by the powerful digestive juices. 



The remaining appendages of the cephalothorax are the pair of 

 pedipalpi and the four pairs of walking legs. The former are situ- 

 ated on each side of the mouth and resemble the legs closely except 

 for size and for lack of the metatarsal segment. In the female, the 

 pedipalp is a simple appendage terminated ordinarily with a single 

 tarsal claw, but in the male the distal end is the seat of the special 

 copulatory organ of that sex. The role of the palpi in mating will 

 be mentioned later. 



Four pairs of legs are always present, as in typical arachnids. 

 Each leg consists of seven segments, called beginning with the one 

 that fits snugly into the sternal space coxa, trochanter, femur, pat- 

 ella, tibia, metatarsus, and tarsus. At the end of the tarsus are to be 

 found two or three claws. The legs vary tremendously in length 



