800 



CLASS V. ARACHNIDA. 



which we have fossil record, having persisted with compara- 

 tively little change from Silurian times. They inhabit tropical 

 and the warmer temperate countries, e.g. the Mediterranean 

 area, but they are intolerant of the sun and usually lurk in 

 crevices and under stones during the day-time but become 

 active after dusk. Then they seek their food, which mainly 

 consists of insects and spiders. 



The tergum of the prosoma (cephalo-thorax) is somewhat 

 square with often a low median keel. Near the middle line 



are two central separate small 

 eyes and at the edge are two 

 to five lateral eyes (p. 334 ff). 

 Some species are blind. The 

 mesosomatic (pre-abdominal) 

 terga are wide plates separated 

 by soft skin from the ventral 

 sterna. The metasomatic 

 segments (post-abdominal) are 

 encased in chitinous rings; they 

 are compressed and show no 

 trace whatever of soft skin 

 except between each segment. 

 The post -anal poison-sting is 

 bulbous with a sharp point ; 

 close to the tip are two minute 

 openings which communicate 

 with two poison-glands in the 

 bulb. 



The appendages are as fol- 

 lows (Fig. 518) : - 



A. On the prosoma : 

 (i) The chelicerae, small 

 three-jointed, chelate appendages almost hidden under the 

 anterior edge of the prosomatic tergal shield ; the teeth on the 

 claws are of much systematic importance. (ii) The pedipalpi ; 

 these are the well-known six-jointed nippers of the scorpion 

 with powerful chelate terminal claws, their coxae are pro- 

 duced in towards the mouth as a gnathobase. (iii), (iv), (v), 

 and (vi) The walking legs ; they are six-jointed, though a 

 marking in the fourth joint may indicate a seventh ; numbers 



10 



Vm. 519. Ventral view of pro- and meso- 

 soma of Buttius afer (from Leuckart, after 

 Cuvier). 1 Chelicerae ; 2 pedipalpi : 

 3-6 1st to 4th pair of ambulatory legs ; 

 7 genital operculum ; 8 pectines ; 9 

 4 pairs of stigmata on the 3rd-6th meso- 

 somatic region ; 10 1st metasomatic 

 segment. 



