ARACHNIDA. 629 



erally into large ccecal appendages (Fig. 622, 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 body. In the Pedipalpes 

 (Phrynidae 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 thus adapted to their 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 the spiders a brown or dirty 

 yellow 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 closely uni- 

 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 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 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 limb, which does not move horizontally 

 but vertically; behind are the large, well developed maxillae 

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

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

 antennae 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 Arach- 

 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 retain 

 their embryonic position and are grouped with the legs (see 



