OTHER ANIMALS 655 



highly civilized country, but the well-known practical character 

 of the American people is also an element. 



The Breeding Place of Mosquitoes. The post^embryonic de- 

 velopment of the mosquito, that is, the interval between the egg 

 state and the adult winged form, occurs entirely beneath the sur- 

 face of water. The young during this portion of their life-cycle 

 are true aquatic insects with one exception, they do not breathe 

 the air dissolved in the water as do fish, but by a special structure, 

 a respiratory siphon, breathe the free air above the surface of the 

 water; deprived of this they perish. By nature of their structure 

 the young of mosquitoes can develop only in water and then only 

 under certain conditions. As a rule mosquitoes breed in small col- 

 lections of standing fresh water. Specimens are sometimes found 

 in streams and some species are known to breed in salt or brackish 

 water. For all economic purposes the statement is correct that 

 mosquitoes breed only in water, usually stagnant fresh water. Do 

 u.iraij with tliese places and it becomes impossible for mosquitoes to 

 breed. 



Life History of Mosquitoes. The determination of methods 

 for destroying an injurious insect implies a careful study of its 

 life-history in order to find the vulnerable point in the life-cycle 

 of the pest. All insects undergo during their developmental period 

 remarkable changes in form, structure and habits. One can cer- 

 tainly detect no resemblance between the wriggling larva of the 

 mosquito in the water and the adult winged insect in the air. In 

 the higher animals there are no distinct periods or stages of devel- 

 opment. The young on hatching from the egg or at birth resem- 

 ble the parent with the exception that they are smaller in size and 

 undeveloped, but as growth continues they gradually acquire the 

 size and characteristics of the adult. The life history of insects, on 

 the other hand, is, generally speaking, divided into three distinct 

 ,-tages after hatching from the egg; the young or larva, the grow- 

 ing stage in the life of the insect; the pupa, a period of development 

 during which a wonderful change or transformation in the form, 

 structure and habits occurs; and the adult or winged insect, the 

 form we usually recognize. 



The eggs of the common mosquito, Culex, are deposited on 

 the surface of standing water. Under the right conditions of tem- 

 perature they hatch in about twenty-four hours. The larvae de- 

 velop to their full size in the course of eight to fourteen days dur- 

 ing which time they moult or cast off their outer covering several 

 times to provide for increase in size. The development of the 

 larvae depends on the temperature of the water and the food sup- 

 ply. Their food consists of the plant and animal matter, often 

 microscopical in size, common to standing water. The pupa of the 

 mosquito is also aquatic, normally resting inactive at the surface. 

 This is the period during which the mosquito transforms from 

 an aquatic insect to one of the air. The young or growing slauo, 

 has passed. The pupa takes no food and moves only when dis- 

 turbed as a matter of protection. The pupal stage is much shorter 



