INSECTS. 95 



disagreeable or unhealthy products. Others by feeding on insects reduce the number 

 of the forms which injure the crop. 



In their injurious aspects the insects have possibly attracted the most attention, 

 and long statistical tables are frequently published showing the value, in dollars and 

 cents, of the human possessions destroyed by these apparently insignificant forms. In 

 the following pages especial attention will be paid to these noxious insects, and we 

 have here only to instance the grasshopper-plague of Kansas and Nebraska, the damage 

 produced by the Hessian-fly, the onion-fly, and the chinch-bug, and the ravages of 

 the clothes-moth and the carpet-beetle, to call to mind this important aspect of the 

 group. 



In number of species, as well as of individuals, the group Insecta is by far the largest 

 of the divisions of the animal kingdom. It is estimated that from a quarter to half a 

 million distinct forms exist on the face of the globe. These are divided as follows : 

 Myriapoda, 1,000 ; Arachnida, 5,000 ; Neuroptera, 7,000 ; Orthoptera, 7,000 ; Hemip- 

 tera, 10,000; Coleoptera, 125,000; Diptera, 30,000; Lepidoptera, 25,000; Hymneoptera, 

 25,000. Of course these numbers are merely guesses ; but when we consider that nearly 

 100,000 species of beetles are catalogued as being in the various collections of the world, 

 we see that these estimates are probably within limits. The number of individuals is, 

 of course, beyond any possibility of estimation. 



For our purposes we may divide the class of Insecta into four sub-classes: 

 Protracheata, embracing the single genus Perlpatus ; Arachnida, Myriapoda, and 

 Hexapoda, or insects proper. 



J. S. KlNGSLEY. 



FIG. 130. Larva showing abdominal legs. 



