ARACHNIDA. 



447 



and independent movements, and their extremity is commonly armed 

 either with a hook or with a pair of small nippers. 



In spiders the parts called mandibles {^fig. 172, cl) are situated at 

 the front of the head and are terminated by a moveable and very 

 sharp hook, which is pierced at its extremity by a small fissure, 

 serving to give issue to the poison secreted by a gland lodged in the 

 preceding joint. The maxillse (ib. h, h) are two in number, and the 

 labium (ib. e) situated between these organs is composed of a 

 single piece. The maxillary palpi (ib. c), compared with those of 

 insects, are of great length and size, and resemble the thoracic feet, 

 which, in the Mygale, they nearly equal in length. In female spiders 

 they are terminated by a single moveable claw : in the males the last 

 joint (ib. d) is dilated, and presents a more complicated structure. 

 In the scorpion the mandibles {fig. 164, a) are short, and terminate in 

 a pair of strong pincers : the 

 maxillary palpi (ib. 6) are 

 proportionally more deve- 

 loped than in the spiders, and, 

 like the mandibles, they ter- 

 minate by pincers, which are 

 so strong and large in the 

 great scorpion {Biithus Afri- 

 canus), as to resemble the 

 chelae of the Crustacea, and 

 more especially as they are 

 succeeded by four pairs of 

 simple and smaller thoracic 

 legs. 



In the genus Galeodes the 

 mandibles are chelate, but 

 much longer and larger than 

 in the scorpions. The maxil- 

 lary palpi resemble small 

 slender feet, but without the 

 terminal hooks ; and the 

 succeeding pair of append- 

 ages being similarly modi- 

 fied, only six ambulatory 

 feet of the ordinary structure 

 remain. Two rudiments of 

 antennae have been noticed 

 attached to the mandibles in 

 certain species of this genus. 



The head is likewise more distinct 



