VI ARACHNOIDS A— OUTER ORGANISATION 515 



division derived from ancestors. It is also very doubtful whether a 

 ringing of the body, which can here and there be recognised, has 

 anything whatever to do with a true segmentation. 



The body of the parasitic Linguatulidce is elongated, vermiform, and 

 ringed. But this ringing has again nothing to do with a real seg- 

 mentation. 



B. The Extremities. 



The Araehnoidea are typically provided with six pairs of 

 extremities exclusively belonging to the eephalo-thorax. The 

 abdomen is everywhere limbless. 



Of the 6 pairs of extremities the most anterior pair is known as the 

 chelicerae (mandibles, jaw-feelers, elaw-feelers, falees), the second 

 as the pedipalps (underjaws, maxillae). The other 4 pairs are 

 mostly similar in form and serve as ambulatory legs for locomotion. 



The First Pair of Extremities — the ehelieerse — lie in front of and 

 above the mouth. They are either 2- or S-jointed, and serve for 

 seizing, and often also for killing, prey. The terminal joint is claw- 

 like. The cheliceree are chelate, when the terminal claw is, as in the 

 chelate feet of Astacus, movable against a process of the preceding 

 joint; they might be called claw-jaws when the terminal claw can 

 merely be bent round upon the preceding joint, as in the seizing feet 

 of the Stamatopoda. 



The Second Pair of Extremities — the pedipalps or maxillse — 

 lie on the two sides of the mouth, and everywhere function as oral 

 appendages, being nearly always provided with masticatory ridges at 

 their bases. The masticatory ridges, which elsewhere can move freely 

 against one another, have in the Eedipalpi [ThelyphonidcB), Gyphophthal- 

 midce, and Acarina, grown together in the middle line as an adaptation 

 for sucking. As opposed to the masticatory ridge, the remaining part 

 of the second extremity is called the palp or feeler. The many- 

 jointed palp (originally 6-jointed) everywhere serves as an organ of 

 touch, but may perform very different functions as well, and in 

 correspondence with these functions may be very variously modified. 

 In the Scorpionidce, Cherneiidce, and in many mites it ends in pincers 

 and functions as a seizing organ. In the Pedipalpi it ends as a claw 

 feeler with a movable claw. The feelers of the Fhalangidm and of many 

 Acarina have a terminal claw. In the male Araneidce the terminal joint 

 of the feeler is transformed into a copulatory organ. The feelers of the 

 Solpugidce serve, like the 4 subsequent pairs of extremities, for locomotion, 

 and are formed much like the rest. The same is the case in the 3Iicro- 

 thelyphonidce, where the second pair of extremities not only resembles 

 those which follow it, but is even devoid of the masticatory ridges. 



The Third Pair of Extremities lies behind the mouth, and is in 

 most Araehnoidea more or less like the 3 following pairs, and serves, 

 like them, for locomotion. In the Scorpionidce and Phalangidce the 

 basal joint is provided with a masticatory ridge. The third pair of 



