47^ THE INVERTEBRATA 



parts and the second pair of wings are reduced to short clawed 

 structures. Well-known examples are Pseudococcus the mealy-bug, 

 Tachardia lacca the lac-insect of commerce and Aspidiotus perniciosus 

 the San Jose scale-insect of citrus trees. 



Fig- 330- Types of Rhynchota. A, Macrotrista angularis (Homoptera, Cica- 

 didae). B, Aphis rumicis (apterous viviparous female). C, Winged viviparous 

 female of same. B and C, after Davidson. 



The plantlice (Aphididae), Fig. 330, notable for their wide dis- 

 tribution and for their prolific reproduction, have transparent wings 

 and a two-jointed tarsus, that of the Coccidae being one-jointed. 

 Wax-secreting cornicles are borne dorsally in the abdomen. 



In the last family the reproductive phenomena are of immense 

 scientific importance. A comparatively simple life cycle is that of 

 Aphis rumicis. The winter is passed on the spindle tree Euonymus as 

 eggs laid in the autumn after the fertilization of females. In spring 



