INTEODUCTION. 



Insects equal in numbers of species all other living beings, both animals and 

 plants, but systematically they constitute only one of the classes of one 

 of the phyla into which animals are divided. 



PHYLA OP THE ANIMAL KINGDOM. 



Arthropoda: with jointed legs operated by muscles attached directly to the 

 skin or when legless with air tubes or tracheae in every part of the body. 



Chordata: with back bone or in certain aquatic members only a soft noto- 

 chord between central nervous system and body cavity. 



Mollusca: with a shell, or where this is wanting, with a well developed eye. 

 (if shell is composed of a small and a large valve, the latter perforated, it 

 is a Molluscoidea.) 



Echinodermata: body radially arranged. Coelenterata: with a common 

 gastrovascular cavity. 



Protozoa: unicellular. 



Annulata. Porifera: many openings into digestive tract. Platyhelminthes: 

 without anal opening, or with whole surface ciliate. Molluscoidea: ends of 

 digestive tract near together Trochelminthes: with retractile anterior ring of 

 cilise. Nemathelminthes: body unsegmented and mouth region not retractile. 



Insects are by far the most important group of animals In their effects 

 on human interests, excepting only the vertebrates in which man him- 

 self belongs. Entomologists have rendered such signal service in studying 

 and controlling useful and harmful insects that they have generally been 

 called upon to extend their endeavors outside of the class insecta, and to 

 consider all similar matters in other classes or even in other phyla. 



The problems in the other phyla are: for Chordata, the poisons used for 

 killing rodents and birds, which are commonly classed with insecticides in 

 Mollusca, the treatment of snails and slugs attacking plants corresponding 

 with the treatment of insects doing similar Injury, and among the annulata 

 and other worms numerous parasitic forms both on plants and animals 



1 



