116 WHIP-SCORPIONS AND OTHERS 



mirably constructed for sucking the eggs of other minute arthro- 

 pods such as Symphyla and Pauropods, but this hypothesis has 

 been contested. No predators have yet been recorded, although the 

 same author found attached to the ventral surface of the prosoma of 

 certain individuals, an ecto-parasite of unknown nature, the young 

 forms of which were uni-segmented and the adults three-segmented. 

 Of the mating habits and life cycle of the Palpigradi very little is 

 known, though it is believed that individuals can recognise one 

 another by scent. In certain species the males appear to outnumber 

 the females, while in others, such as K. mirahilis^ males are ex- 

 tremely rare. In the young stages oi Prokoenenia wheeleri there are 

 fewer hairs, fewer cheliceral teeth and fewer flagellar segments 

 than in the adults. In certain species, a pair of eversible sacs have 

 been described on each of the fourth to sixth abdominal sternites. 

 These vary in number and position during growth and may re- 

 present a primitive and very simple type of breathing organ. 



Order thelyphonida 



Classification and distribution 



In their general form, the Thelyphonida bear some slight resem- 

 blance to scorpions. They can easily be distinguished, however, 

 by the form of the pedipalps, the first pair of legs and the abdomen, 

 which bears a slender caudal appendage from which the name 

 *whip-scorpion' is derived. These strange Arachnids are generally 

 of large size, varying from 25 to 70 mm in length. The elongated 

 prosoma is covered by a dorsal carapace and has three thoracic 

 sternites. The chelicerae are composed of two segments and are 

 not chelate, while the pedipalpi are powerful limbs of six segments. 

 Their coxae are fused below the mouth and have no masticating 

 function, but each trochanter has a large semicircular process on 

 its inner side armed with sharp teeth. The processes can be 

 pressed against each other and are well adapted to crushing the 

 prey, which is detected by the long anterior legs. These are not 

 used for walking but are held stretched out in front as tactile 

 organs. There is one pair of median and three pairs of lateral eyes 

 but these are feeble and serve only to distinguish between light 

 and darkness. 



