3180 THE JOINTED ANIMALS 



hand, there is no such distinct head, while antennae are wanting; the first pair of 

 appendages being composed of two or three segments only, and acting as seizing or 

 biting organs. These mandibles are, in fact, the only limbs that can be described 

 as jaws. It is true that the basal segments of the second, and sometimes of the 

 third and fourth, pairs of limbs are used for crushing prey; but their remaining 

 segments nearly always form leg-like appendages, used both for locomotion and 

 grasping. In scorpions, for instance, the limbs of the second pair are converted into 

 large pincers; while in spiders they are short, and resemble the other limbs. In 

 scorpions and the other groups, where these limbs form prehensile weapons, they 

 are called chelce / whereas in the spiders and ticks, where they are smaller and tactile 

 in nature, they are known as palpi. Behind the palpi or chelae come four pairs of 

 limbs, acting as the locomotor organs. The palpi or chelae are typically composed 

 of six segments, and armed with a single claw, which, however, may be fused with 

 the terminal segment, as in scorpions. The legs seem primarily to have been six 

 jointed; and their segments, from base to apex, are respectively termed coxa, 

 trochanter, femur, patella, tibia, tarsus. One or more of these is, however, almost 

 invariably divided^so that the number rises to at least seven. Thus, whereas in the 

 scorpions the tibia, and in spiders the tarsus, is divided, in other groups, like the 

 Pedipalpi, the tarsus may be composed of a number of small segments. Accord- 

 ingly, six pairs of large appendages are attached to the fore part of the body; and 

 since this part was supposed to represent the combined head and thorax of insects, 

 it is termed the cephalothorax. The abdomen may bear small, dwarfed limbs, as in 

 scorpions and spiders, but its limbs are never, either structurally or functionally, 

 like those of the cephalothorax. Although it may be undivided, this part never 

 contains more than twelve segments, and often much fewer. Allowing twelve to 

 the abdomen, and six to the cephalothorax, the body of the more typical members 

 of the class comprises eighteen segments. All Arachnoids breathe air, either by 

 means of short sacs or of long tracheal tubes communicating with the exterior by 

 apertures {stigmata) on the lower surface of some of the abdominal segments. The 

 young which, save in scorpions, are born in the egg stage, resemble their parents, 

 and in the course of growth only undergo a series of molts without metamorphosis. 

 The class may be divided into eight orders, the first of which includes 



THE SCORPIONS Order SCORPIONES 



In this group all the typical eighteen segments of the body are developed, al- 

 though the last five are abruptly narrowed to form with the telson, or poison sting, 

 the tail. The whole abdomen, including the tail, is distinctly jointed; but the 

 cephalothorax is covered above with a single plate or carapace, bearing the eyes. 

 The latter vary from six to ten, two being placed together in the middle, and the 

 others arranged at the sides of the fore part of the carapace. Of the appendages, 

 the four hinder pairs are similar, being tipped with a pair of claws, and used for 

 locomotion. The two front pairs, however, have been transformed into pincers or 

 nippers, the first pair, or mandibles, being small and three jointed, and the second, 



