740 
RHYNCHOTA. 
PHYTOPHTHIRES 
The smaller Homoptera, of the families Cercopidce and Membracidce , 
lead into a series in which the active habits of the larger Homoptera are 
replaced by a method of life in which the insect is more or less fixed with 
a closer ‘ parasitism ’ of the host plant than occurs in the more active 
forms and in which there is a tendency to the development of wingless 
forms, cidminating in completely apterous, usually inactive females. 
Correlated with this is a growing differentiation of the inactive pupal 
stage, leading to the almost wholly inactive male 4 pupa ’ of Coccidce. 
Taking these together, there is sufficient justification for separating off 
as a single group the dimerous and monomerous families of Homoptera , 
with a clear understanding that they are not so widely separate from the 
trimerous families as perhaps the Coccidce themselves are from the dimer¬ 
ous families. It is probable that strictly we should separate the Coccidce 
as a division equal in value to the two, Trimera and Dimer a, but this 
would be for our present purpose inconvenient. An obvious structural 
character separating the Phytophthires from the Homoptera is the 
antenna, in the former long, usually with 8 to 10 distinct joints, in the 
latter short, with a basal joint and a bristle-shaped process. 
Phytophthires , as here constituted, are marked by modifications of 
habits and structure which accord with a more specialised parasitism 
to their host plant; in the Psyllidce we get flat inactive scale-like forms, 
often gall-insects, in which locomotion is greatest in two stages, the very 
young larvae and the winged males and females, but which does occur 
in all stages; in th eAphidce, the phenomenon of parthenogenesis appears, 
combined with the viviparous habit and the apterous female adult, but 
this is combined with winged males and females and production of 
fertilised eggs ; the apterism, viviparism and parthenogenesis displayed 
are found when abundant food and suitable climate are favourable to 
quick reproduction and an easy life on the growing plant, when 
locomotion is not required and the organism devotes itself to its 
parasitic activities ; when these conditions disappear, the characters of 
the higher, less degraded organism are developed to meet the less easy 
conditions of life. 
In Aleurodidce, the active periods are limited to the young nymph and 
the winged adult, both sexes are winged and egg production is the rule; 
but the parasitism shows itself in the reduction of moults (as in all of this 
