2o8 ARTHROPODA 



Patten considers that Paleozoic Eurypterids have scorpions as their 

 survivors and that the Ostracoderms represent their fossil descend- 

 ants, which led towards the true Vertebrates. (See page 219.) 



Trilobita. — The extinct trilobites (Figure 97) were dominant 

 species in the Cambrian period, but disappeared in the Carboni- 

 ferous. The limbs resembled those of Crustaceans and antennae 

 were present. It has been suggested that trilobites descended from 

 a stock common to Arachnoidea and Crustacea. 



Arachnoidea. — The scorpions are represented in the Silurian 

 rock by fossil forms similar to those now living. All living Arach- 

 noidea are represented in Tertiary deposits. Crustacea are abun- 

 dant as fossils, from the early Paleozoic. Myriapoda are found 

 from the Devonian. Insecta appeared in the Pennsylvanian. 



