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TEXT-BOOK OF ZOOLOGY 



ever, also be produced on leaves as a diseased condition in the form 



Ai'i'Lii Kaiik Plant Lolne, on 

 Woolly Aphis (American Blicht). 



Colony of insects on an apple-tree, with 

 dill'erent "forms" produced in 

 course of year. 



(Letters explained in text.) 



of a sacchariferous secretion.) The func- 

 tion of two tubular organs, or " cornicles," 

 near the end of the abdomen is not yet 

 definitely ascertained. They are called 

 " honey-tubes," but do not separate the 

 sugary secretion. 



The plant lice first met with in spring 

 are produced from eggs which have sur- 

 vived the winter. They are all females, 

 and, like the succeeding generations, are 

 for the most part wingless. In about ten 

 days they have already reached maturity, 

 and without previous copulation with males 

 bring forth a number of living young 

 (" parthenogenesis "). These also are 

 females, which go on producing females 

 asexually until the autumn. Only the de- 

 scendants of the last generation of the 

 latter are winged males and females. These 

 (being winged) extend the range of the 

 species, and after copulating produce eggs 

 which are not injured by the winter cold. 



A much-dreaded species of plant louse 

 is the so-called Woolly Aphis (Sehizoneura 

 lanigera), which when crushed leaves a red, 

 blood-like stain, hence called "blood-louse " 

 in Germany. It lives on the bark of the 

 apple-tree, and by sucking the sap produces 



