182 



ANNULOSA. 



and the segments of the abdomen carry legs. As is the case 

 with all the air-breathing Articulates, the remains of Arachnida, 

 though of considerable theoretical interest, are of very rare 

 occurrence as fossils. They will therefore be very briefly 

 noticed here. Of the groups of the Arachnida, the Mites 

 (Acarida), the Harvest-spiders (P/ta/angida),ihe Rook-scorpions 

 (PseudoscorpionidcR), the Scorpions (Pcdipalpi], and the true 

 Spiders (Araneida), have all been detected in a fossil condition. 

 The three first groups require no consideration here, being 

 almost unknown except as occurring in amber, which is a fossil 

 resin of late Tertiary age. The Scorpions and Spiders both 

 appear to have come into existence in the Carboniferous period, 

 and the forms which then existed do not appear to have been 

 strikingly different from living types. 



ORDER PEDIPALPI. The typical members of this order are 

 the Scorpions (Scorpionidce), in which the abdomen is distinctly 



Fig. 125. Cydophthalmus senior. A fossil Scorpion from the Coal-measures of Bohemia. 



segmented, and not separated front the thorax by any marked con- 

 striction. The respiratory organs are in the form of pulmonary 

 sacs opening on the under surface of the abdomen by distinct 

 apertures or " stigmata." The jaws (maxillae) carry an enor- 



