828 CLASS V. ARACHNIDA. 



and the first and second pair of legs, and of two free segments,, 

 those of the third and fourth pair of legs (Fig. 545 C, a, 6, c). 

 According to Wheeler there are eleven abdominal segments ; 

 the first is small and forms the wasp-like waist, and the last 

 three, the 9th, 10th and llth (Fig. 545 C, 8, 9, 10) are also 

 contracted. The last bears the post-anal multi-segmented 

 flagelliform telson (comparable with that of Thelyphonus) with 

 some fifteen joints, which probably have not the value of true 

 segments. 



The chelicerae are three- jointed and terminate in a scissor- 

 like fang. The pedipalpi are nine- jointed ; the first pair of 

 legs is the longest and has twelve joints, the second and third 

 have the more usual Arachnid number of seven joints, and the 

 last has eight. The appendages do not appear to have any 

 gnathobases ; they arise w r ell to the side of the ventral surface- 

 and their bases are separated by distinct sternal plates. 



There are no eyes, but certain sensory organs occur on the- 

 cephalo thorax and there are numerous hairs of systematic import. 

 The crescentic mouth guarded in front by the epistome and 

 behind by the hypos tome opens into a chi tin-lined pharynx.. 

 This passes into an oesophagus which pierces the chief nerve- 

 mass and immediately enlarges into a sucking-stomach which is 

 dilated by muscles running from it to the exoskeleton of the 

 cephalo thorax. This stomach opens by a valvular orifice into 

 the intestine which gives off a pair of diverticula before leaving 

 the cephalo thorax. In the abdomen, the intestine enlarges and 

 in the third to the seventh segments inclusive it gives off a pair 

 of shallow diverticula. No malpighian tubules are present and 

 no salivary glands. The intestine opens into a rectum which 

 terminates in an anus. A pair of coxal glands occur in the 

 cephalothorax and are said to open in front of the third pair of 

 legs. 



In Prokoenenia three pair of lung-sacs have been described, one 

 on the fourth, one on the fifth and one on the sixth abdominal 

 segments, but the evidence that they are more respiratory in/ 

 function than the protrusible and retractile vesicles in the 

 Collembola is yet to seek. No definite heart has yet been 

 described. 



The nerve-ganglia are highly concentrated ; the supra- oeso- 

 phageal and sub-oesophageal ganglia are fused into a large mass- 



