A SPIDER 25 



segment being the one next to the last. The basal segment of 

 the pedipalp is called the maxilla. The two maxillae are flattened 

 structures situated on the underside of the cephalothorax just 

 back of the mandibles, their forward, medial margins, which cover 

 the mouth, being used to lacerate and squeeze the food so that 

 the animal juices can be sucked up. Spiders prey exclusively 

 upon living animals ; but they can take in only liquid food. 

 The pedipalps of the female spider differ in shape from those of 

 the male, and the two sexes may be distinguished in this way. 

 In the female the pedipalp looks exactly like a small leg; in 

 the male the terminal portion is expanded and very complex in 

 structure, being used by the animal in the act of pairing. 



The third, fourth, fifth, and sixth pairs of appendages are the 

 legs, each of which is composed of the following seven segments : 

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

 The legs are used by the spider for a variety of purposes besides 

 walking. They are important as tactile organs, their great length 

 increasing their usefulness in this respect, and they undoubtedly 

 compensate the animal in a certain degree for the lack of an- 

 tennae. They are also of use in spinning and manipulating the 

 web, the complex structure of the claws being associated with 

 this function. 



The median plate between the maxillae on the ventral side of 

 the body is the labium ; the one between the bases of the legs is 

 the sternum. 



The abdomen. The dorsal surface is usually marked by several 

 pairs of depressions which mark the points of attachment of mus- 

 cles. At the hinder end, on the ventral surface, are three pairs 

 of spinnerets. Study these carefully with the aid of a hand lens. 

 At the end of each spinneret are numerous microscopic holes, 

 from which is exuded the semifluid silk. This is made up of 

 many soft strands, which harden as they unite to form the thread. 



A study of the embryology of the spider shows that the spin- 

 nerets are homologous to abdominal legs. 



