6 OUTLINES OF ENTOMOLOGY. 



variable, and in some species the division is into three regions, as in 

 insects, while others bear some resemblance to spiders in the arrange- 

 ment of the joints. In the framework of the worms we find numerous, 

 joints, but no distinct head, thorax or hind body. 



Another and very interesting peculiarity of insects is found in 

 their transformations or metamorphoses. Insect life begins with an 

 embryo contained in an egg. From this egg hatches the first active 

 form, which is called a larva (plural larva), the term signifying a mask, 

 because the true form of the insect is considered to be masked or con- 

 cealed at this stage of life. All caterpillars, grubs and maggots are 

 larvse. When the larva is full grown it changes, in most cases, to a 

 very different object, and is then termed a pupa (plural pupce), from a 

 word meaning a doll or mummy, in reference to its quiescence and the 

 swathed or bandaged appearance of its members. From the pupa in 

 due time emerges the perfect insect or imago (plural imagines], which is 

 the final form and the one in which it possesses wings, unless it be- 

 longs to the few wingless species. 



The chief office of the perfect insect is to develop and lay the- 

 eggs from which another generation of larvae will hatch, and, in the 

 case of some species, to provide food for their young. 



To britiy recapitulate, in answer to our opening question: An 

 insect is an articulate animal having the external skeleton composed of 

 a number of rings or joints, which are separated into three groups to- 

 form a distinct head, thorax and abdomen. It has six legs, and, in its. 

 perfect state, has two or four wings, and is further characterized by 

 changes of form and habit called metamorphoses. 



The science which treats of the structure, habits and classification 

 of insects is called Entomology, a term composed of two Greek words 

 which signify a " discourse on insects." 



Economic Entomology has for its object the investigation of the 

 habits of injurious insects, with a view to the better preservation of 

 our persons and property from their attacks. It also includes experi- 

 ments with such species as are or may prove to be valuable for their 

 products or properties, and endeavors to ascertain which are indirectly 

 useful to man on account of their parasitic and cannibalistic habits. 



