ARACHNIDA. 629 



erally into large ca3cal appendages (Fig. 022, alimentary canal 

 of Tegenaria civilis ; a, stomach, witli coeca ; c, liver ; cl, renal 

 organ; e, fat bod^'), and then passes into a short, small intes- 

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

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

 not having any coecal dilatations to the very small stomach. 



The salivary glands are often of large size, especially in 

 Ixodes, and are thns adapted to Ihcir blood-sucking 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 tli& spiders a brown or dirty 

 3'ellow mass filling a large part of the abdominal cavity and 

 enveloping most of the other viscera. 



As during the growth of the young spider the head is thrown 

 back on top of the thorax to which it is thus most closelj^ uni- 

 ted, it follows that the simple ej-es, from two to twelve in 

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

 thorax, while no other sensory organs, /. e.,the compound eyes 

 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 what is originally the proper or normal site of the 

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

 most authors to homologize them with the antennae of hexa- 

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

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

 Thus the month-opening is ))rouglit far forward ; it is flanked on 

 each side by a mandible (Plate 10, fig. 3, c, o, moval)le claw, or 

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

 but vertically ; behind are the large, well developed maxilhB 

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

 their long, leg-like i)al[)us. Thus the function of the insectean 

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

 Claparede's researches on the emliryology of the spiders and 

 mites have demonstrated that tlie front pair of legs of Aracb 

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

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

 embryonic life thrown forwards, and associated with the max- 

 illiE and other moutli-parts, while in the Arachnids they retoin 

 their embryonic position and are grouped with the legs (see 



