8 



ELEMENTARY ENTOMOLOGY 



beneficial, though they feed on beneficial as well as on injurious 

 insects, while scorpions are found only in tropical countries and 



are chiefly a nuisance on account 

 of their poisonous sting. 



The Myriapoda include the myri- 

 apods and centipedes, commonly 

 called thousand-legs. Their body 

 consists of a distinct head and a 

 long abdomen, all of the segments 

 of which are similar, and each of 

 which bears a pair of legs, so that 

 they are readily distinguished from 

 all other arthropods. In many ways 

 the myriapods are more closely re- 

 lated to the insects than either of 

 the other classes mentioned above. A few species sometimes 

 injure vegetables or fruits lying on or in the ground, and these 

 are considered as within the 

 sphere of economic entomol- 

 ogy ; but for the most part 

 myriapods are harmless, al- 

 though the house centipede 



FIG. 5. A spider ; a typical arachnid 



FIG. 6. A myriapod 



is a nuisance and is abhorred by the 

 housekeeper. Some of the tropical 

 myriapods reach relatively enormous 

 size, being several inches long, and 

 bear poison fangs in connection with 

 the mouth-parts. 



The Insecta, or Hexapoda, include 

 the true insects, which form the largest 

 group of animals as far as both the 

 number of different species and the 

 number of individuals are concerned. 

 About 300,000 different species have 

 already been described, while there is 



FIG.;. A parasitic fly, showing babl total f l oooooo speci es 



parts or a typical insect 



in existence. The known species form 



ant, antennae; //, head ; /, thorax; 



abd, abdomen ; -wg, wings ; /, legs over four fifths of the total number of 



I 1 



