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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



pretarsus is found also in a few adult i)terygote insects, as in the 

 Coccidae. Pediculid^e. and the mammal-infesting Mallophaga. hut the 

 structure of the foot in such cases has probably resulted secondarily 

 from the suppression of one claw in an original pair of claws. 



The pretarsus of an adult insect, in its typical form (fig. 36 A, B), 

 arises from the end of the last tarsal segment by a membranous base, 



Cla 



Fig. 36. — Structure of the insect foot (pretarsus). 



A, end of tarsus (Tar) and foot of a roach (Periplancta amcricana), dorsal 

 view: claws {Cla) articulated to unguifer process {k) on end of last tarsal 

 segment; arolium (Ar), a median lobe between claws. 



B, the same, ventral view; showing ventral pad (in) of arolium, auxiliary 

 plates (/) at bases of claws, and unguitractor plate (Utr) to which is attached 

 tendon (.r) of retractor muscles of claws (fig. 39, A'). 



C, foot of a cicada (Tibicina scptctidecim) : arolium lacking, or represented 

 by small plates (n) between claws. 



D, foot of an asilid fly, lateral view : arolium lacking ; lateral, lobe-like 

 pulvilli (Pv) arising from auxiliary plates (/) beneath claws, and median 

 spine-like empodiumi (Emp) arising from unguitractor plate. 



E, the same, ventral view. 



upon which are supported a pair of movable lateral chnvs (Cla), and 

 a median lobe, the arolium (Ar). The claws are hollow, multicellular 

 organs, their cavities being continuous at their bases with the lumen 

 of the base of the pretarsus. Each is articulated dorsally to the 

 unguifer (A, k), a median process of the distal end of the last tarsal 

 segment (Tar). The arolium, likewise a hollow lobe, is a direct 

 continuation of the median part of the pretarsal base ; it may be 

 entirely membranous, or its walls may be partly chitinous. On the 



