ARACHNIDS, CE NTIPEDES, AND MILLIPEDES— ARTHROPODS 207 



rest for a week or so, molt, and climb another bush and again take up 

 its patient vigil. This may be repeated several times during the life of 

 the tick and germs ingested along with the blood of one host may be 

 transferred to a later host. Texas cattle fever is a serious disease that 

 infects cattle, and expensive dipping of cattle for tick eradication is a 

 necessity in many of the cattle-raising regions of the country. Spotted 

 fever is a serious human disease which people may develop from bites 

 by ticks that have previously fed on infected rodents. Tularemia is 

 another disease which people may take from ticks that have fed on 

 infected animals. 



The king crab or horseshoe crab is a salt water animal that is found 

 along the Atlantic Coast from Maine to Yucatan, Mexico. It is some- 

 times classed as an arachnid, but some authorities prefer to put it in a 

 separate class of its own. It bears a superficial resemblance to some 

 of the true crabs. Instead of book lungs, as in the spiders, the king 

 crab has book gills which are in full view on the underside of the 

 abdomen and obtain oxygen from water rather than air. King crabs 

 are mild, inoffensive creatures with small, weak claws. They feed on 

 almost any sort of small animal which they can overpower. Their 

 larvae are very primitive and are known as trilobite larvae because they 

 closely resemble an extinct group, the Trilobita. Because of this re- 

 semblance it is generally believed that king crabs are descended from 

 these fossil creatures. 



Class — Chilopoda 



The name centipede means "hundred legs," but the number of legs 

 in these animals may vary from 30 to more than 400 in different species. 

 The body of a centipede consists of loosely jointed segments with a 

 pair of legs on each segment except the first and the last. The first 

 segment bears a pair of vicious-looking fangs that are connected with 

 poison sacs and can inflict a painful bite. There is a widespread super- 

 stition that a person's flesh will rot and fall off if a centipede runs 

 across it, and another that a centipede can inject poison from its legs. 

 Both are without foundation in fact. The author has seen centipedes 

 in the Southwest measuring up to eight inches long, and tropical forms 

 are known which are up to a foot in length. Most of those in the 

 United States, however, are much smaller and are beneficial because 

 of the large number of insects which they eat. The house centipede is 

 a species with rather long legs that may often be seen in human dwell- 

 ings. Like other centipedes they come out at night in search of food, 

 and their presence is often unknown until they may be discovered in 



