CLASSIFICATION AND DISTRIBUTION 109 



make up a family. Thus the grasshoppers of the genus 

 Melanoplus and those of all the other genera having short 

 antennae combined with certain other characters in common, 

 are placed in the family Locus'tidae. The katydid and other 

 green grasshoppers, with many meadow species, belong to 

 an entirely different family. The crickets (Gryl'lidae) and 

 the cockroaches (Blat'tidae) are allied to both of the grass- 

 hopper families. By common consent family names end in 

 -idae. Families are united to form orders, and orders in turn 

 make up classes. The largest and most important of the 

 orders which make up the class Hexapoda have already 

 been discussed. As we shall see later, the classes are united 

 to form phyla (sing., phylum), the primary divisions of the 

 animal kingdom. 



The Simplest Insects. In the study of insects we began 

 with the grasshopper because it is large enough to study 

 easily. There are two orders of insects which are even 

 simpler in structure than the grasshoppers and therefore 

 are said to be "lower" than the Orthoptera. These are the 

 Thysanu'ra, or fish moths, and the Collem'bola, or spring- 

 tails. The insects of both these orders lack wings altogether. 

 In their development these lowest insects have no metamor- 

 phosis, for the young immediately upon leaving the eggs 

 are almost exactly like their parents. Because of their sim- 

 ple structure many people believe that these are much like 

 the insects which first appeared upon the earth in some past 

 geological time. 



Thysanura. Glue is frequently eaten off the bindings of 

 books, and wall paper is often loosened from the walls, by a 

 minute, wingless, silvery insect, the fish moth, or silverfish 

 {Lepis'ma sacchari'na, Fig. 66). In spite of their small size 

 and retiring habits, they may cause great damage to libra- 

 ries and in households because of their appetite for paste, 

 starch, and such substances. 



