no ZOOLOGY. 



After hatcliiiig from the egg, insects pass through a 

 series of changes of form called a metamorphosis. Tlie 

 butterfly passes through four stages: 1, the egg; 2, the 

 caterpillar or larva; 3, the chrysalis or piipa; and, 4, the 

 imago or adult insect. In the grasshopper the j^erfect or 

 ftdult insect differs chiefly from the larva in having wings; 

 in such insects the metamorphosis is said to be incomplete; 

 while the butterfly and bee have a complete metamorphosis, 

 the larva or caterpillar being entirely unlike the imago or 

 perfect insect. 



Insects are both useful and injurious to vegetation. 

 Were it not for certain bees and moths, orchids and many 

 other plants would not be fertilized; insects also assist in 

 the cross-fertilizution of plants. For full crops of many of 

 our fruits and vegetables, we are lai-gely indebted to bees, 

 flies, moths, and beetles, which, conveying pollen from 

 flower to flower, ensure the production of abundant seeds 

 and fruits. Mankind, on the other hand, suffers enormous 

 losses from the attacks of injurious insects. Within a 

 period of four years, the Eocky Mountain locust, migrating 

 eastward, inflicted a loss of 1200,000,000 on the farmers of 

 the West. In the year 1864 the losses occasioned by the 

 chinch-bug in the corn and wheat crop of the valley of the 

 Mississippi amounted to upward of $100,000,000. It is 

 estimated that the average annual losses iu the United 

 States from insects is about 1100,000,000. On the other 

 hand, hosts of ichneumon flies and Tachina flies reduce 

 the juiniljers and usually prevent undue increase in the 

 numbers of injurious insects. 



The number of species of insects in collections is about 

 200,000. Of those there are about 2r),000 species of Hijme- 

 nopiera (bees, wasps, etc.); a)jout 2."),o()0 species of Lepi- 

 doptera (butterflies and moths) ; about 25,000 Diptera (two- 

 winged flies), and 90,000 CnlvDjttera (beetles); with about 

 4G00 species (A Aracluuda (spiders, etc.), and 800 species 

 Qf MtjrioiKida (iniHepedes, centipedes, etc.). 



/usccts ;ire ttistributed all over the surface of the earth. 



