THE APPENDAGES. 



21 



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

 chanter; the femur; the tibia, and, lastly, the tarsu,, which is 

 subdivided into from one to five joints, the hitter being 

 tlie normal number. The terminal joint ends in a i)air 

 of claws between which is a cushion-like sucker called 

 the pulviUas. 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 

 nn.st 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 Chironomns (Fig. 26), in ^Vhich the 

 prothoracic pair of legs is reduced to inarticu- 

 late fleshy legs like the abdominal ones. 



The 2^osition of the different i):nrs of legs 

 deserves notice in connection with the principle 

 of " antero-posterior symmetry." The fore- ^ 



leo-s are directed forwards like the human arms, '?• -'• 



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

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

 out life ; in the lower Ilexapods, 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 Neuropterons larv.^ {Phryganea, Coryclahis, etc.) the 

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

 "•inal forceps" of the adult insect. They sometimes become 

 true, many-jointed appendages, and are then rc-markably like 



Kio ■>'■> A coxa; B, tro.hantev: C, femur; 1), tibia; F, tibial spurs; E, tarsus, 

 d.vided into five tarsal joints, the filth eucUng m a cUw.-From Sa,iborn. 



