vi AEACHNOIDEA OUTER ORGANISATION 513 



is distinctly segmented and consists of twelve segments. In it, again, 

 we can distinguish two divisions, distinctly marked off from each other. 

 The anterior division, the broad pre-abdomen, consists of 7 segments ; 

 the posterior, slenderer, tail-like division, the 

 post-abdomen, of 5 segments. At the end of 

 the post-abdomen is found the poison sting 1 , 

 which is often included as one of the segments. 

 It ought, however, probably to be considered 

 as an articulated appendage of the last seg- 

 ment, the latter being recognised, as in all 

 Arthropoda, by the position of the anus. 



Two small, insufficiently known groups of Arach- 

 iioidea, the Tartaridce and Microthelyphonidee, appear, 

 as far as the metamerism of the body is concerned, 

 to occupy in some respects an intermediate position 

 between the Solpugidce and the Scorpionidce, and in 

 others between the latter and the Thelyphonidce. In pjg. 360. Chelifer Bravaisii 

 the Microthelyphonidce an anterior and a posterior (after Cuvier, Regne animal). 

 division can be distinguished in the cephalo-thorax, 2 ' 6 > Second to sixth pairs of 

 and again, the latter shows on its dorsal surface indis- e 



tinct division into three parts which recalls the arrangement of the cephalo-thorax of 

 the Solpugidce. The abdomen consists of ten segments, the last three being much 

 narrower and smaller than the rest and representing a sort of post-abdomen, whose 

 terminal segment carries a long, thin, jointed caudal filament. In the Tartaridce, the 

 thorax is divided by a distinct circular constriction into an anterior and a posterior 

 division. The abdomen consists of seven or eight segments followed by a small, 

 short, truncated post-abdomen, formed of a few (four) segments and carrying a 

 variously -shaped caudal appendage. 



In the Pedipalpi the cephalo-thorax is unsegmented. The abdomen 

 consists of 12 segments (Thdyphonus) or of 11 (Phrynus). In Thelyphonus 

 the last 3 segments are very small and narrow, and form a sort of 

 post-abdomen, which carries an anal filament. 



The cephalo-thorax of the Chernetidce (Pseudoscorpionidce), which 

 recall the Scorpionidce in their general type, is unsegmented or else has 

 2 dorsal transverse furrows. The abdomen consists of 11 (less often 

 10) segments. A pre-abdomen and a post-abdomen cannot be dis- 

 tinguished, and a poison sting or a caudal or anal filament is wanting. 



The cephalo-thorax of the Phalangidce (including the Cyplioplithal- 

 midce) is unsegmented. The abdomen, which is sometimes clearly, 

 sometimes indistinctly segmented, is applied to the cephalo-thorax along 

 its whole breadth. There is no separation of the abdomen into pre- 

 abdomen and post-abdomen, and no caudal filament. 



In the Araneidce (the true spiders) the cephalo-thorax as well as 

 the abdomen is unsegmented. The two are separated by a deep 

 constriction. 



In the Acaridce the segmentation of the body as well as its division 

 into regions is suppressed. It is rightly assumed that the un- 

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