274 



COLLEGE ZOOLOGY 



Carapace 

 Pedipalp 



Pedipalp 



Chelicera 



Walking 

 leg 



Telson 



Genital 

 operculum 



Book gills 



Walking 

 leg 



Limulus 



(Horseshoe crab) 



ventral view 



Scorpion 

 dorsal view 



Figure 166. Horseshoe crab, Limulus, (formerly Xiphosura); ventral view. Natural size about 

 15 inches long. It is called a living fossil because it has undergone little change during long geologic 

 periods. Scorpion, dorsal view. The poison gland is contained in the telson. 



curious and include a sort of dance. Scor- 

 pions are viviparous. The young ride about 

 upon the back of the female for about a 

 week and then shift for themselves. They 

 reach maturity in about 5 years. 



Scorpions are one of the oldest forms of 

 life still found on this earth. Fossilized 

 specimens from many parts of the world 

 show that they have remained essentially 

 unchanged for hundreds of millions of years. 

 Fossil scorpions resemble present-day forms 

 (Fig. 166) in possessing a pair of chelicerae, 

 a pair of pedipalps, four pairs of legs, and a 

 poison gland. Thus it can be seen why mod- 

 ern scorpions may well be described as "liv- 

 ing fossils." 



Mites and ticks 



Mites and ticks (Fig. 167) are found al- 

 most everywhere. Some live in fresh water, 

 others in salt water; some live on the ground, 

 others on vegetation; some live on the out- 

 side of the bodies of other animals, and 

 others burrow into them. Animals and 

 plants, either living or dead, serve as food 

 for them; the parasitic species live largely 

 on blood. The common names of certain 

 families (p. 279) give some idea of the dif- 

 ferent types of ticks and mites. Some of 

 those important to man are described be- 

 low. 



