The External Anatomy of Spiders 



formed of a single sclerite, which is usually more or less movable, 

 and which on account of its position has been termed the lower 

 lip or labium. Like the rostrum, the labium is situated between 

 the second pair of appendages, the pedipalps (Fig. 87), the ros- 

 trum occupying a more dorsal position, and the labium, a more 

 ventral one. 



The labium of a spider is not homologous with the labium 

 of an insect, which is formed of a pair of united appendages. 



The Mouth. — The mouth cavity is situated between the 

 base of the pedipalps, which form the sides of this cavity. The 

 roof of the mouth is formed by the epipharynx; and the floor 

 by a sclerite, the tip of which lies upon the labium. 



The mouth is fitted for the reception of only liquid food. 

 The spider cuts and presses its victim; and when it is sucked dry, 

 the hard parts are thrown away. 



The Pedipalps (ped'i-palps). — The second of the two pairs 

 of appendages of the head are the pedipalps. They are situated 

 one on each side of the mouth; and are more or less leg-like in 

 form, especially in females. By some writers these appendages 

 are termed the maxilla?; but as they are not homologous with 

 the maxillae of insects, this is an undesirable use of the term. 



Each pedipalp consists of a series of six segments which are 

 named, beginning with the one next to the body: coxa, trochanter, 

 femur, patella, tibia, and tarsus (Fig. 88). These terms are the 

 same as those applied to the corresponding segments of the leg. 

 The pedipalps differ from the legs in that the tarsus consists of 

 a single segment, there being no metatarsus; and there is never 

 more than one tarsal claw, which is wanting in all males and in 

 the females in many genera. 



A special set of terms for the segments of the pedipalps has 

 been much used and is included here for reference. According 

 to this system the basal part is termed the maxilla and the fol- 

 lowing segments, beginning with the trochanter, are designated 

 as the axillary, humeral, cubital, radial and digital. 



The endites. — In the tarantulas, except Atypus, the coxa 

 of the pedipalps closely resembles the coxa of a leg (Fig. 88); 

 but in the true spiders the coxa bears a plate, which is the crushing 

 part of the organ, this plate is the endite (Fig. 89, en). On 

 the dorsal surface of the organ there is a suture separating the 

 endite from the basal part of the coxa. This suture is present 



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