150 TRANSACTIONS OF THE ILLINOIS 



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without winged individuals, of one or both sexes, during some portion of 

 the year, although brood after brood lives and dies with all its members 

 wingless. The very great similarity of the wingless individuals of the 

 different groups renders any specific characters derived from their color, 

 markings, etc., often of doubtful value; and this fact has so impressed 

 itself upon the casual and ordinary observers that they usually designate 

 them, no matter where found or what their habits, by the common name. 

 Plant-lice, as though all belonged to one species. Naturalists have there- 

 fore sought some more positive method of distinguishing species from 

 each other ; this has been found in their habits. It was the belief of the 

 immortal Linnaeus that every plant supported a distinct species of Aphis, 

 or, in other words, that a species of Aphis inhabited but one species of 

 plant : and Curtis, the great English entomologist, tells us that, after 

 careful and extensive examination of this subject, he is inclined to sub- 

 scribe generally to this opinion, adding that, although a species of 

 Aphis is limited to a certain plant, yet there may be more than one 

 species of plant-louse to one plant. As I will speak farther on of the use 

 to be made of these facts, I will omit further mention of them now, 

 except simply to remark, that while a large number of species are naked, 

 there are many others more or less covered when young, or during life, 

 with a cottony or downy substance, on which account they are often 

 called "Woolly Plant-lice," a very appropriate name. 



One of the strangest facts connected with the history of these insects 

 is their method of reproduction. But in order to understand this, it is 

 necessary to give a brief account of their life-history through one year. 



These insects, as likewise all other species belonging to the Order 

 Homoptera, undergo only a partial metamorphosis or transformation, that 

 is to say, they never are worms or grubs, and never undergo those re- 

 markable changes which transform the grub into a beetle, and the cater- 

 pillar into a butterfly. The larvae and pupis are similar to the perfect 

 insect in form and habits ; and although they frequently cast their skins, 

 and the winged specimens gradually acquire these organs, there is no 

 true dormant pupae or chrysalis state, as we find in many other insects. 

 Their whole lives are therefore devoted to imbibing food, and producing 

 new broods. 



In the autumn, as a general and almost universal rule, the last brood 

 consists of winged specimens, both males and females. These pair, soon 

 after which the male dies ; the female deposits her eggs, after which she 

 also dies. Early in the spring, as soon as the sap begins to flow, these 

 eggs hatch, and the young lice at once insert their tiny beaks into the 

 bark or leaf on which they are situated, and begin to pump up the sap. 

 They wander but little, their entire time being devoted to feeding ; hence, 

 they grow rapidly, and soon come to maturity. This spring brood con- 

 sists, generally without an exception, of females without wings. These 

 females, by some strange provision of nature, are capable of reproducing 

 their kind without the intervention of males, and, instead of depositing 

 eggs, as the last fall brood, are usually viviparous, bringing forth living 

 larvae. These are likewise all females, similar to those from which they 



