ARTHROPOD A 201 



of twenty-four hours showed that the digestive tract is destroyed in 

 that time, and that all soft parts of the body cavity are disintegrated 

 in forty-eight hours. The geranium is particularly attractive to the 

 Japanese beetle. 



Class 5. Arachnida. — These air-breathing Arthropoda have no 

 antennae, or true jaws; have the head and thorax fused into a 

 cephalothorax; and at the posterior part the abdomen; and have 

 four pairs of walking legs, with their first pair of appendages de- 

 veloped into nippers, or chelicerae. They include spiders, mites, 

 ticks, scorpions, and the king crab. 



Scorpionidae. — The scorpions are found in warm regions hiding 

 away during the day and coming forth at night to prey on insects 

 and spiders, which they sting with their poison fang at the tip of the 

 abdomen. The sting of an ordinary scorpion of three or four inches 

 has been compared with that of a hornet. Patten believes that 

 scorpions are descended from the fossil Merostomata {Eurypterida). 

 (See pages 207, 218.) 



Phalangidea. — The harvest men or " daddy-long-legs " have 

 extremely long legs and a segmented abdomen. They feed on 

 living insects. 



Acarina. — The common red mite and the " red spider " of green- 

 houses attack plants. The chiggers or harvest mites attack mam- 

 mals, including man, burrowing into the skin and causing much 

 irritation. The follicle mite, Demodex folliculorum, invades the hair 

 follicles of mammals and man, producing black heads. The itch mite 

 is a parasite of the epidermis. The scab parasite, Psoroptes com- 

 munis, produces sores on cattle and horses. 



Ticks are responsible for the transmission of a number of diseases. 

 The cattle tick, Boophilus {Margaropus) annulatus, is the medium of 

 transfer of a sporozoan, Piroplasma bigeminum, which causes Texas 

 fever. In Africa, a common tick, Ornithodorus moubata, has habits 

 like a bed-bug and causes relapsing fever. 



Older Araneida. (Spiders.) — Spiders (Figure 94) are among the 

 most interesting of the Arthropoda. They construct webs, using two 

 kinds of silk, one dry and inelastic, the other viscid and elastic. 

 Spiders use silk to construct webs, to build tents or nests, and also 

 in locomotion. Man uses spider threads for cross-hairs in his 

 telescopes. Spiders are Arachnids, with the abdomen separated 

 distinctly from the cephalo-thorax, but the segments of each region 

 closely fused They have four pairs of legs and two pairs of mouth 



