INTRODUCTION 5 



c. Antennae with eight to ten segments; rostrum with three 

 segments, reaching to mesocoxae; metacoxae near together, 

 about length of their coxae apart; adults always provided with 

 wings, veins arising as branches from both sides of a short 

 median proximal stem; nymphs with body usually strongly 

 depressed, wing pads horizontal and usually ending beyond 



the body. PSYLLIDAE. 



cc. Antennae with three to six segments; rostrum with four or 

 five segments, reaching to and frequently beyond the mesocoxae ; 

 metacoxae distant, four or five times as far apart as the length 

 of their coxae; adults winged or wingless, veins arising as 

 branches from the caudal margin only of a large cephalic vein; 

 nymphs with body cylindrical, rarely depressed, wing pads not 



horizontal and usually held against the body APHIDIDAE. 



bb. Wings membranous and rarely absent in adult; metathoracic 

 wings subequal in size to mesothoracic; body of adult and wings 

 always densely covered with a fine white, powdery wax; nymphs 

 and adults sometimes closely associated, always different in form, 

 adults insect-like, nymphs always scale-like or grub-like in form 

 and never covered with a white waxy powder, frequently with 

 marginal plates of wax, always without antennae and legs, and 



abdomen always provided with a vasiform orifice ALEYRODIDAE. 



aa. Tarsi of the adult rarely with more than one segment and always 

 with a single claw, legs frequently wanting; wings, when present, 

 two in number; eyes in adult and nymphal female never compound 

 and frequently wanting, wanting in nymphal male and rarely com- 

 pound in adult male; rostrum very short, rarely reaching mesocoxae 

 or as far as metathoracic spiracles if mesocoxae are wanting in fe- 

 male, wanting in older nymphal stages and always in adult male and 

 rarely wanting in adult female; adult male usually winged and 

 insect-like, adult female scale-like, grub-like, or gall-like in form, 

 frequently inbedded in mass of wax of its own excretion, frequently 

 fixed to the food plant and immovable; legs and antennae frequently 

 greatly reduced in size, rudimentary, or wanting in nymphal and 



adult females; abdomen never provided with vasiform orifice 



COCCIDAE. 



The members of the family Coceidae live upon the stems, 

 leaves and roots of plants. While a great majority of the species 

 are fixed to the host-plant for at least a part of their life, some 

 are always active. The fixity or quiesence of the different species 

 is confined for the most part to the female sex and is always 

 associated with the production of eggs and young. There is the 

 greatest diversity in the external form of coccids. This is due 

 more to the form of the waxy excretion with which the body is 

 covered than to the general form of the body itself. The amount 

 of wax and the form it assumes are also associated with repro- 

 duction. There is frequently considerable variation in the external 



