580 ARTHROPODA. 



but terminate in claws or in imperfect pincers, and the abdomen 

 does not terminate in a " sting." The existing genus Phrynus has 

 been detected in Tertiary deposits, while the recent genus Thely- 

 phonus is represented in the Carboniferous rocks by the genus 

 Geralinura. 



5. Araneida. — This division of the Arachnida includes the true 

 Spiders, characterised by the soft and imperfectly segmented ab- 

 domen, which carries two, four, or six " spinnerets " posteriorly, and 

 is united in front with the cephalothorax by a constricted peduncle. 

 The maxillary palpi are slender and leg-like, and never terminate in 

 nipping-claws, while the "falces" or "mandibles" are hooked, and 

 contain a poison-gland in their base. The most ancient represen- 

 tatives of the Spiders, so far as at present known, are the Protolycosa 

 anthracophila, and Phalaranea borassifolia of the Coal-measures of 

 Europe, both of which have been referred to the section of the 

 Territelarice. No Mesozoic Spiders have hitherto been discovered ; 

 but about seventy genera have been recognised as occurring in 

 Tertiary deposits — many of them in amber. About one-half of the 

 known Tertiary genera of Spiders are without representatives at the 

 present day. 



Class III. Myriopoda. 



The class of the Myriopoda includes the multisegmentate, worm- 

 like Arthropods known as the Centipedes and Millepedes, and is 

 characterised by the fact that the head is distinct ', and the remainder 

 of the body is divided into 7iearly similar segments, the thorax exhibit- 

 ing no clear li?ie of demarcation fro7ii the abdomen. There is one pair 

 of antennce, and the number of the legs is always more than eight pairs. 

 Respiration is by trachece. 



In this class of the Arthropoda the head is always distinctly 

 marked off from the rest of the body, and consists of five or six 

 amalgamated somites. The head carries a single pair of jointed 

 antennae, which are usually simple (fig. 436), but are bifid, and 

 carry many-jointed appendages in the aberrant genus Pauropus. 

 Behind the antennae there is generally a variable number of simple 

 sessile eyes. The mouth is placed on the under side of the head, 

 and is provided with mandibles and maxillae. The Centipedes also 

 possess two pairs of " foot-jaws," of which the hindmost pair (fig. 

 436,/) are of large size, and are terminated by perforated hooks, 

 which communicate with internally-placed poison-glands. These 

 appendages, however, are not carried upon the head, but are 

 attached to a special segment formed by the amalgamation of the 

 anterior thoracic rings. The segments behind the head are numer- 

 ous, and there is no distinct line of demarcation between those 



