196 AN INTRODUCTION TO ZOOLOGY. 



basin and a skewer. This, with some fossil types 

 which are related to it, forms a separate group, the 

 Xiphosura or Gigantostraca, which used to be classed 

 with the Crustaceans. Prof. Ray Lankester, however, 



Fig. 55.— The King^-crab (lunulus moluccanus). 



has transferred it to a position near the Spiders, with 

 which it is linked by the Scorpions, under the name 

 of Hcematobranchia. Limulus has two compound 

 eyes, and two simple eyes. 



The rest of the Arthropods are included under the 

 name of Tkacheata, because they breathe through 

 tubes called trachese. These include, besides the 

 insects, class Hexapoda, also the Millipedes, class 

 Myriopoda, and a class called Peototeacueata, which 

 consists only of one genus, Perlpatus. This name has 

 been given to it because Peripatus is believed to re- 

 semble the archaic type from which the rest of the 

 Tracheata have been derived. It has a distinct head, 

 with one pair of antennae and two eyes, and from 

 fourteen to over thirty pairs of short legs, which 

 differ from those of the Centipedes in having bifid 



