AGRICULTURAL ENTOMOLOGY. 



tnM^ of natural history which treats of insects. Agricultural 

 itj^Bon to such insects as injure the field and garden crops, 

 laras, r 



Entomology is that depart 



entomology limits its invest 



household possessions, orchftfflS, forest trees, and domestic animals of farmers and gar 

 deners. The number of species that subsist mainly or entirely at the expense of 

 cultivators, is much larger than one would suppose who had not made these destructive 

 animals and their ravages the subject of particular study. Baron Kollar, following 

 generally the arrangement of Latreille, treats of insects injurious to agriculturists 

 under twelve orders. Dr. Harris is less comprehensive in his plan, confining his 

 treatise to insects injurious to vegetation ; but he is more thorough and practical, so far 

 as he goes. 



Having on another occasion briefly described the twelve orders of Kollar, we 

 shall now attempt a definition of the six orders, to the discussion of which Dr. H. has 

 devoted an octavo volume of some 500 pages. The names of these orders are : 

 CoieojJtera, Orthoptera, Hemiptcra, Le]3idoptera, Hymenojitera, and Diptera. Before 

 proceeding to describe the several orders named, it may not be amiss to state that the 

 word " insect" is derived from the Latin insecure, to cut into, or notch ; most insects 

 being almost severed at the points where the head is joined to the thorax, and the thorax 

 to the abdomen, as in the ant and honey-bee. Insects do not breathe through their 

 mouth, but have several air holes called spiracles on each side of their bodies, usually 

 nine in number, for the free ingress and egress of the atmospheric air, needed to purify 

 their blood. The brain of an insect is small ; and instead of a spinal marrow, a kind 

 of knotted cord extends from the brain to the hinder extremity ; and from the knots on 

 this cord and the brain issue numerous small, whitish threads, which are nerves, and 

 spread over the animal system. A few water insects breath by means of gills. The 

 heart is a long tube lying under the back, having little holes on each side for the 

 admission of the juices of the body, which are prevented from escaping again by valves 

 or clappers, formed to close the holes within. By the appropriate arrangement of 

 valves, the blood flows toward the head, and is prevented from passing in an opposite 

 direction. The blood is either colorless or a yellowish fluid, and does not circulate in 

 proper arteries and veins ; but, being driven to the head by the contraction of the tubu- 

 lar heart, it is discharged into the fluids derived directly from the digestive organs, and 

 is again oxygenated by contact with the air pipes, and finally it returns into the tubular 

 heart for continued circulation. Insects have no internal skeleton like the vertebrata. 



Order 1. Coleop)tera. The word chosen to designate insects of the first order is 

 formed from koleos, a sheath ; pteron, a wing. [We have no Greek type.] The idea 

 conveyed is, that all insects of this order have theu- wings in a sheath, or more properly 



