638 ZOOLOGY SECT. 



rudiments of them have been found in the larvae of some species. 

 The first pair of appendages of the cephalothorax (probably repre- 

 senting the antennae of the Crayfish) are the chelicerce ; the second 

 are the pedipalpi, the representatives of the Crayfish's and Cock- 

 roach's mandibles. Behind these are four pairs of legs. The 

 organs of respiration are sometimes tracheae, similar to those of 

 the Insects, sometimes book-lungs sacs containing numerous 

 book-leaf-like plates : sometimes leaf-like external appendages 

 or gills. 



1. EXAMPLE OF THE CLASS. THE SCORPION (Euscorpio or 



Buthus). 



Scorpions are inhabitants of warm countries the largest kinds 

 being found in tropical Africa and America. They are nocturnal 

 animals, remaining in holes and crevices during the day, and 

 issuing forth at night to hunt for their prey, which consists of 

 Spiders and Insects. These they seize with their pincer-claws 

 and sting to death with their caudal spine, afterwards sucking 

 their juices. 



There are a number of different species of Scorpions, divided 

 into several genera, which differ from one another in comparatively 

 unimportant points, so that the following general description will 

 apply almost equally well to any of them. 



External features. A Scorpion (Fig. 543) has a long narrow 

 body, in superficial appearance not unlike that of a Crayfish. 

 There is a small cephalothoracic shield or carapace, covering over 

 dorsally a short anterior region cephalothorax or prosoma. This 

 is followed by a long posterior region or abdomen, the terminal 

 part of which in the living animal is habitually carried over the 

 back (Fig. 546), constituting the " tail," at the end of which the 

 sting is placed. The carapace bears a pair of large eyes about its 

 middle, and several pairs of smaller eyes on the antero-lateral 

 margin. The anterior, broader part of the abdomen, which is 

 termed the pre-abdomen or mesosoma, consists of seven segments, 1 

 each of which is enclosed in firm, chitinous, dorsal and ventral 

 plates, or terga and sterna. The tergum and sternum of each 

 segment are separated from one another laterally by intervals 

 of soft skin, except in the seventh, where they are united laterally 

 for a longer or shorter distance. The posterior, narrower part of 

 the abdomen, known as the post-abdomen or metasoma, consists of 

 five segments, each enclosed in a complete investing ring of hard 

 chitinous matter. Articulating with the last segment of the 

 post-abdomen is a terminal appendage, the caudal spine or sting, 

 swollen at the base and acutely pointed at the apex, where open 



1 Originally there are eight, but the original first loses its distinctness in 

 embryonic life. 



