18 OUTLINES OF ENTOMOLOGY. 



successive stages of development being marked only by the acquisition 

 of certain organs and appendages. 



The most familiar example of complete transformation is afforded 

 by an insect which in its first active state is a sluggish, worm-like cater- 

 pillar, feeding voraciously on herbage, and changing in due time to the 

 inactive, casket-like chrysalis, which bears as little resemblance to the 

 larvaj that preceded it as to the imago that shall ultimately escape from 

 it, viz., the broad-winged, bright-hued butterfly, instinct with graceful 

 activity, as it hovers over the flowers from which it sips is sole nourish- 

 ment, a dainty draught of nectar. Examples of partial transformation 

 are found in such insects as grasshoppers, locusts, true bugs, etc. 



The life of an insect begins with the embryo contained in an egg. 

 Instinct guides the parent insect in the placing of her eggs, so that her 

 progeny, as soon as hatched, find themselve surrounded with the kind 

 of food they require. The eggs of insects are of various forms — round, 

 oval, conical or disk-like. They are deposited singly or in clusters ; 

 sometimes openly exposed on the surfaces of leaves or stems, some- 

 times concealed with the utmost ingenuity. Those of many species are 

 beautifully colored or elegantly sculptured. The eggs of some small 

 insects which produce but few are proportionately large, while on the 

 other hand many large insects lay very minute eggs, but make up in 

 number what is lacking in size. 



The insect in hatching from the egg enters on its larval stage of 

 existence. This is the form in which all actual growth takes place, and 

 in which, as a consequence, the insect requires most food. It may, in 

 succeeding stages of development, assume different forms and acquire 

 additional members, but it never really increases in bulk. 



The larvae of the various kinds of insects differ so much in appear- 

 ance, and in many other respects, that it is difficult to give a list of 

 characters that are common to all. The typical form is more or less 

 worm-like: i. e., cylindrical and elongate; but the variations from this 

 type are exceedingly numerous, even among insects whose transforma- 

 tions are complete; while those that undergo only partial transforma- 

 tion do not conform to it at all. 



In the majority of larvse the thorax and abdomen are not distinct, 

 except that the first mentioned region is often provided with the rudi- 

 ments of legs. The latter are of a shelly texture, small and pointed at 

 the extremity, with three or four joints. They are six in number, and 

 arc termed the true or thoracic legs, to distinguish them from the fleshy 

 disks called false legs or prolegs, which in many species support the 

 hinder part of the body. 



