THE APPENDAGES. 



21 



pieces, i.e. the coxa and trochantine (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 

 the normal number. The terminal joint ends in a pair 

 of claws between which is a cushion-like sucker called 

 the pulvillus. This sucking disk enables the Fly to 

 walk upside down and on glass. 



In the larva, the feet are short and horny, and the Fig. -25. 

 joints can be still distinguished. In Myriopods, 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 different pairs of legs 

 deserves notice in connection with the principle 

 of " antero-posterior symmetry." The fore- 

 legs are directed forwards like the human arms, Fl &- 2f5 - 

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

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

 out life ; in the 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 ; they constitute the 

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

 true, many-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 filth ending m a claw. from Sariborn. 



