The External Anatomy of Spiders 



with the second antennae of Crustacea, but not with the antennae 

 of insects.* 



It has been supposed by many writers that the chelicerae 

 correspond to the mandibles of insects, and they have, therefore, 

 been called mandibles, a term that cannot properly be applied to 

 them. The term fakes, proposed by Blackwall in 1852, is also 

 used by many writers, but there is no good reason for discarding 

 the much older term chelicerae. 



The lateral condyle of the chelicera. — In many spiders there 

 is at the base of each chelicera, on the lateral face, a smooth 

 prominence, an articulating condyle (Fig. 80, / c); this may be 

 termed the lateral condyle of the chelicera. This condyle is wanting 

 in many families; and its presence or absence is a useful character 

 in classification. It is sometimes called the basal spot of the 

 chelicera. 



When the condyle is present, the margin of the clypeus is 

 usually marked with a dark spot at the point of articulation 

 with the condyle. 



The furrow of the chelicera. — Usually there is a furrow in the 

 basal segment of the chelicera for the reception of the claw when 

 it is closed (Fig. 81); and often there is on one or both sides of this 

 furrow a row of teeth (Fig. 83). 



In the tarantulas, where the claw moves vertically, the 

 gins of this furrow may be designated as the inner and the outer 

 respectively; in the true spiders, as the upper and the lower. 



The scopula (scop'u-la). — Frequently there is on the upper 

 side of the furrow of the chelicera, a brush of hairs (Fig. 82, 5); 

 this is the scopula of the chelicera. Scopulae are found also on 

 other appendages. 



The rake of the chelicera. — In certain tarantulas that burrow 

 in the ground the extremity of the basal segment of the chelicera 

 is armed with several rows of strong teeth, which are used by the 

 spider in excavating its burrow; these constitute the rake of the 

 chelicera (Fig. 83). 



The claw of the chelicera. — The claw of the chelicera is very 

 hard, curved, and pointed. On its concave face, there are usually 



• In the Crustacea (lobsters, crabs, and allies) there are two pairs of antenna?, the first antenna 

 or antennules and the second antenna, commonly called the antennae. In spiders the first antenna: 

 are lost, appearing only in the embryo; and the second antenna; are modified into prehensible organs, 

 the chelice.ae. In insects the first antennae are retained and function as feelers, while the second 

 antennae are almost invariably lost: they are retained, however, in a vestigial condition in some 

 Thysanura. 



IOO 



