THE APPENDAGES. 21 



pieces, i.e. the coxa and trocliantine (see Fig. 12); the tro- 

 chanter; the femur ; the tibia., and, lastly, the tarsus, which is 

 subdivided into from one to five joints, the latter being qa 

 the normal mimber. The terminal joint ends in a pair ^ 

 of claws between which is a cushion-like sucker called J/d 



the pidvillus. This sucking disk enables the Fly to 

 walk upside down and on glass. 



In the larva, the feet are short and horny, and the rig. 25. 

 joints can be still distinguished. In Mjaiapods, each segment 

 of the abdomen has a pair of feet like the thoracic ones. We 

 must consider the three pairs of spinnerets of Spiders, which 

 are one to three-jointed, as homologous with the jointed limbs of 

 the higher insects. In the six-footed insects (Hexapoda), the 

 abdominal legs are deciduous, being present in the Coleopterous 

 grub, the Dipterous maggot, the caterpillar, and larva of the 

 Saw-fly, but disappearing in the pupa state. They are often, 

 as in most maggots, either absent, or reduced in number to the 

 two anal, or terminal, pair of legs ; while in the Saw-flies, there 

 are as many as eight pairs. These "false" or "prop-legs" 

 are soft and fleshy, and without articulations. At the retrac- 

 tile extremity is a crown of hooks, as seen in caterpillars or the 

 hind-legs of the larva of Chironomus (Fig. 26), in which the 

 prothoracic pair of legs is reduced to inarticu- 

 late fleshy legs like the abdominal ones. 



The position of the difierent pairs of legs 

 deserves notice in connection with the principle 

 of " antero-posterior symmetry." The fore- 

 legs are directed forwards like the human arms, ^'S- '^^■ 

 but the two hinder pairs are directed backwards. In the Spiders, 

 three pairs of abdominal legs (spinnerets) are retained through- 

 out life ; in tlie lower Hexapods, a single pair, which is ap- 

 pended to the eleventh segment, is often retained, but under 

 a form which is rather like an antenna, than limb-like. In 

 some Neuropterous larvae (Phryganea, Corydalus, etc.) the 

 anal pair of limbs are very well marked ; tliey constitute the 

 " anal forceps " of the adult insect. They sometimes become 

 true, manj^-jointed appendages, and are then remarkably like 



Fig. 25. A, coxa; B, trochanter ; C, femur; D, tibia; F, tibial spurs ; E, tarsus, 

 divided into five tarsal joints, the fifth ending in a claw. — From Sanborn, 



