CLASSIFICATION AND ORIGIN OF INSECTS 1421 



acquires wings, but is very sluggish, broad, more or 

 less flattened, and in fact, when full grown, looks 

 like a small brown, red, or white scale. 



The larvae of the order Lepidoptera are familiar 

 to us all under the name of caterpillars. The in- 

 sects of this order in their larval condition are 

 almost all phytophagous, and are very uniform 

 both in structure and in habits. The body is long 

 and cylindrical, consisting of thirteen segments; 

 the head is armed with powerful jaws; the three 

 following segments, the future prothorax, meso- 

 thorax, and metathorax, each bears a pair of simple 

 articulated legs. Of the posterior segments, five also 

 bear false or prolegs, which are short, unjointed, 

 and provided with a number of booklets. A cater- 

 pillar leads a dull and uneventful life; it eats raven- 

 ously and grows rapidly, casting its skin several times 

 during the process, which generally lasts only a few 

 weeks; though in some cases, as, for instance, that of 

 the goat-moth, it extends over a period of two or 

 three years, after which the larva changes into a 

 quiescent pupa or chrysalis. 



Fossil insects are, unfortunately, rare, there being 

 but few strata in which the remains of this group 

 are well preserved. Moreover, well-characterized 

 Orthoptera and Neuroptera occur as early as the 

 Devonian strata; Coleoptera and Hemiptera in the 

 Coal-measures; Hymenoptera and Diptera in the 

 Jurassic; Lepidoptera, on the contrary, not until 

 the Tertiary. But although it appears from these 

 facts that, as far as our present information goes, 

 the Orthoptera and Neuroptera are the most ancient 



