118 ORDER HEMIPTERA 



the venation in some genera. The forms with the most 

 numerous veins are the more primitive and the fe\ver-^■eined 

 forms must be regarded as speciaHzed. 



The nectaries, or so-called "honey tubes" or "cornicles," 

 are structures peculiar to Aphididse, located on the hinder 

 part of the abdomen. Fluids may exude from their tips and 

 much difference of opinion has existed as to their functions. 

 Some think that the fluids are used as a means of defense. 

 It is now generally accepted that the "honey dew" emitted 

 by plant lice is discharged from the anal opening, and con- 

 sists of slightly modified sap from the plant to which the 

 aphid is attached. It is sweet and may form some sugar on 

 evaporation and is much sought by ants and some other 

 insects. 



Aphids are characterized by the appearance of several 

 successive generations which are devoid of wings and closely 

 confined to their host plant. Reproduction is in large 

 measure parthenogenetic, many generations occurring with- 

 out the appearance of the sexual forms. A rapid rate of 

 reproduction is provided for; sometimes as many as ten or 

 twelve generations in a season. It has been estimated that, 

 starting with one stem-mother in the spring, her progeny 

 during the season, if not curtailed, would amount to bil- 

 lions or trillions of individuals, sufficient to overrun the 

 world or to equal in bulk of organic matter the population 

 of China. The agamic eggs are termed "pseudova," and 

 are often developed and hatched before being extruded 

 (ovoviviparous). 



No general statement can be made which will properly 

 cover the life history and development of all species, but in 

 general, and in the temperate latitudes particularly, hiber- 

 nation takes place in the egg stage. As the usual thing these 

 eggs are fertilized and occur on the plant which was the last 

 host of the species in the autumn. In the spring these eggs 

 hatch into stem-mothers, which are asexual individuals and 

 for which there is no corresponding male. They do not 

 require fertilization and they produce either eggs or living 

 young. The young produced are ordinarily wingless when 



