156 AN INTRODUCTION TO ENTOMOLOGY. 



than in either of the two preceding families. The first pair of wings 

 is larger than the other ; and the two wings of each side are usually 

 connected by a compound hooklet. The beak is two-jointed, and 

 varies greatly in length ; sometimes it is longer than the body. The 

 compound eyes are prominent ; and ocelli are also usually present. 

 The antennae are from three- to seven-jointed. On the dorsal aspect 

 of the sixth abdominal segment there is, in many species, a pair of 

 tubes, through which a sweet, transparent fluid is excreted. In 

 some genera these organs are merely perforated tubercles ; while in 

 still other genera they are wanting. 



The fluid which is excreted through the abdominal tubercles is 

 the substance known as honey-dew. It is sometimes produced in 

 such quantities that it forms a glistening coating on the leaves of 

 the branches below the plant-lice, and stone walks beneath shade- 

 trees are often densely spotted with it. This honey-dew is fed upon 

 by bees, wasps, and ants. The bees and wasps take the food where 

 they find it, paying little, if any, attention to its source. But the 

 ants recognize in the plant-lice useful auxiliaries, and often care for 

 them as man cares for his herds. This curious relationship will be 

 more fully discussed under the head of ants. 



In addition to honey-dew, many Aphids excrete a white sub- 

 stance. This may be in the form of a powder, scattered over the 

 surface of the body, or it may be in large flocculent or downy 

 masses; every gradation between these forms exists. 



The plant-lice are remarkable for their peculiar mode of 

 development. The various species differ greatly in the details 

 of their transformations ; but the following generalizations can be 

 made. 



At some period eggs are produced by impregnated females. 

 This ordinarily occurs in the autumn ; in which case the eggs do not 

 hatch till the following spring. From the fact that these eggs are 

 fertilized, they are frequently referred to as true eggs, in contradis- 

 tinction to pseudova, described later. These true eggs are also 

 known as winter eggs. 



From the winter eggs there hatch in the spring a generation of 

 Aphids in which there is no distinction of sex. All are females ; 

 and each has the power of reproducing without the intervention of a 

 male. Such reproduction is termed agamic * reproduction, or repro- 

 duction by budding. And this term is also applied to the individu- 



* Agamic: a (a), without; gamos (yajuoS), marriage. 



