l!:^0 THE HISTORY OF CREATION. 



tliemselves, however, have in some cases disappeared, and in 

 others become transformed into the vAngs of the Flies. They 

 have disappeared entirely in the classes of Spiders and 

 Centipedes, and these groups must accordingly be conceived 

 of as degenerated or peculiarly developed lateral branches of 

 the Fly class, which at an early period branched off from 

 the common primary form of Flies ; Spiders probably did so 

 at an earlier period than Centipedes. Whether that common 

 primary form of aU Tracheata, which in my General Mor- 

 phology I have named Protracheata, did develop directly out 

 of genuine Ringed worms, or at first out of Crustacea of the 

 Zoea form (Zoepoda, p. 177) will probably be settled at some 

 future time by a more accurate knowledge and comparison 

 of the ontogeny of the Tracheata, Crustacea, and Annelida. 

 However, the root of the Tracheata, as well as that of the 

 Crustacea, must in any case be looked for in the group of 

 Ringed worms. 



The genuine Spiders (Arachnida) are distinguished from 

 Flies by the. absence of wings, and by four pairs of legs ; 

 but, as is distinctly seen in the Scorpion-spiders and Taran- 

 tulse, they, like Flies, possess in reality only three pairs of 

 genuine legs. The apparent "fourth pair of legs" in spiders 

 (the foremost) are in reality a pair of feelers. Among the 

 still existing Spiders, there is a small group which is prob- 

 ably very closely allied to the common primary form of the 

 whole class ; this is the order of Scorpion-spiders, or Solifugse, 

 (Solpuga, Galeodes), of which several large species live in 

 Africa and Asia, and are dreaded on account of their poison- 

 ous bite. Their body consists — as we suppose to have been 

 the case in the common ancestor of the Tracheata — of a head 



