ARACHNIDA. 6^9 



erally into large coecal appendages (Fig. C22, alimentary canal 

 of Tegenaria civilis ; a, stomach, with coeca ; c, liver ; d, renal 

 organ; e, fat body), and then passes into a short, small intes- 

 tine, going straight to the end of the bod^'. In the Pedipalpcs 

 (Phrynidie and Scorpions) the intestinal canal is more simple, 

 not having any ccEcal dilatations to the very small stomach. 



The salivary glands are often of large size, especiall}' in 

 Ixodes, and are thus adapted to their blood-sncking habits, 

 much saliva being needed to mix with their food. In the 

 spiders and scorpions the liver is well developed and distinct 

 from the intestinal tube, being in the spiders a brown or dirt3' 

 yellow mass filling a large part of the abdominal cavity and 

 enveloping most of the other viscera. 



As during the growth of the j'oung spider the head is throv/u 

 back on top of the thorax to which it is thus most closely xxm- 

 ted, it follows that the simple eyes, from two to twelve in 

 number, are situated on the upper surface of the cephalo- 

 thorax, while no other sensory organs, i.e., the compound ey(>s 

 and antennae, are ever developed. Thus in the adult spider 

 the mandibles seem to be pushed far in front of the ocelli, and 

 to occupy Avhat is originally the proper or normal site of the 

 ocelli, and in insects of the antenniB, which no doubt has led 

 most authors to homologize them with the antennai of hexa- 

 podous insects. Claparede says ''all the appendages are post- 

 oral, hence there are no organs homologous with the antenna?." 

 Thus the mouth-opening is brought far forward ; it is flanked on 

 each side by a mandible (Plate 10, fig. 3, c, a, movable claw, or 

 fang), a large, powerful liml), which does not move horizontally 

 but vertically ; behind are the large, well developed maxilhi) 

 (Plate 10, fig. 2, & ; 7, maxillary palpus ; 8, male palpus), with 

 their long, leg-like palpus. Tluis the function of the insectean 

 antennjB must, in the spiders, reside in the maxillary palpi. 

 Claparede's researches on the embryology of the spiders and 

 mites have demonstrated that the front pair of legs of Araeh 

 nids are homologous with the labial palpi of insects, which, 

 as we have previously stated (p. 59), in the latter, are late in 

 embryonic life thrown forwards, and associated with the max- 

 illae and other mouth-parts, while in the Arachnids they retoin 

 their embryonic position and are grouped witli the legs (see 



