36 ANIMAL BIOLOGY 



tions, and generally upon the approach of cold weather 

 in the fall, broods consisting of both males and females 

 appear, constituting the so-called sexual generation. The 

 females of this generation produce eggs of unusually 

 large size which require to be fertilized before they develop. 

 These eggs remain over winter and hatch out in the follow- 

 ing spring into females which start a new series of par- 

 thenogenetic generations. Aphids are frequently attended 

 by ants which imbibe a sweet liquid called honey dew 

 which comes from the aphid's abdomen. 



One of the most injurious of the aphid family is the 

 Phylloxera which attacks the grape vine. In France 

 especially, enormous injury has been done by this insect. 

 It attacks both the leaves and the roots, producing peculiar 

 galls in each, and causing the deterioration and often the 

 death of the vine. Comparative immunity from these 

 insects has been secured by grafting French vines upon 

 vines native to America. The aphis which feeds upon 

 roots of corn commonly lives in underground galleries 

 of ants. The ants uncover the roots in their burrowing, 

 carry the aphids to them, gather their eggs and carry 

 them to places of safety; in return for these services the 

 ants feed upon the sweet fluid derived from their adopted 

 companions. 



The most degenerate of all of the Hemiptera are the 

 scale insects or Coccidae. In a typical scale bug, such as 

 the San Jose scale, or the apple-tree bark louse, the female 

 is attached to a particular spot on a leaf or twig where 

 she sucks in sap through her slender beak. In the scale 

 bug, legs, wings, antennae and eyes are lacking, and the 

 body is covered by a scale, which is formed by a secretion 

 from certain glands. The female lays large numbers of 

 eggs which hatch into active young furnished with six 

 legs, antennae, and various special organs not found in 



