ARTHROPODA. 195 



a place of safety. Probably the popular superstition, 

 that it is unlucky to kill a spider, was invented by 

 some one who had watchea this proceeding. A home 

 may easily be made for a spider out of a little box, 

 and it makes a very interesting pet. 



The Scorpionldea also have lungs ; but they have 

 the segments of the abdomen not fused, but single, 

 the last six, diminished and elongated, forming a tail. 

 Above this lies a round abdomen, also composed of 

 distinct segments, and distinct from the thorax, which 

 bears appendages. The chelicerw are developed into 

 strong pincers; the poison gland, unlike that of the 

 spider, is in the tail. The breathing organs, called 

 lung-books, consist of chambers containing num- 

 bers of flat plates ; though adapted to breathe air, 

 they are considered to be comparable with the " gill- 

 books " of Liimulus (see below). There are several 

 pairs of eyes. 



The Pseudo scorpionldea, Mock-scorpions, or Book- 

 Scorpions, are so called because they live in old 

 books. They are minute mite-like creatures, with no 

 tail and no sting. The common one, Ghelifer, so 

 called from its scorpion-like claws, has two eyes ; 

 some others have four : they breathe by trachece, or 

 tubes, like insects. 



Limulus, the King-crab, is a creature from the In- 

 dian and Atlantic Seas which may be seen in most 

 large aquaria, and which from the shape of its shell 

 and tail gives one the general impression of a crab 

 that has armed itself for war with an inverted pudding 



