244 
formed. This must have been on a side branch and it gave rise 
to the Cicadidae, Cercopidae, and Membracidae, as well as to 
the Sternorhynchi. The latter followed certain lines of evolution 
of their own, such as specialization by reduction, the formation 
of a setal chamber or crumena and the detachment of part of 
the head capsule from the rest of the head. This reduction may 
be due to their decrease in size together with their sedentary 
habits. The formation of the setal chamber may be for a 
mechanical perfection for controlling the long setae when in 
- use, as well as for a place of protection when at rest. This line 
of evolution of the Sternorhynchi culminates in the Coccidae, 
which are in general the smallest and most sedentary of the > 
group. 
The venation of the early Hemiptera approached Comstock’s 
theoretical wing very closely, and a somewhat similar type of 
venation is found in the more generalized of each of the larger 
groups. The tendency for the bases of the four chief systems 
to amalgamate one with another is traced through all the groups, 
especially with the reduction of the width of the wings. This 
is carried to its greatest extent among the Sternorhynchi and 
is possibly a result of reduction of size and disuse. 
According to my interpretation of the evolution of the Ful- 
goroidea, the Tettigometridae represent the modifed descend- 
ants of the most primitive fulgorids. They descended from a 
form having small hind coxae, as in Cercopidae, and not from a 
form having the present membracid-cicadellid type. The Cixi- 
dae represent a branch from the early stem which have retained 
certain primitive characters, such as the three ocelli, a simple 
venation and the complete ovipositor. At an early period the 
Cixiidae divided into two groups, Cixiinae and the Meenoplini.' 
From the former the Delphacidae arose by the acquisition of a 
mobile spur on the hind tibia; they carried over and retained 
the complete ovipositor and the more generalized male genitalia. 
The modification of the venation in the family is by reduction. 
The Tropiduchidae evidently came from a Cixiinae stock and 
have undergone considerable evolution within the family (if all 
the genera contained in it represent a monophyletic group). 

1 It is possible that this dichotomy goes back to a pre-cixiidae form, 
and that they should be regarded as distinet families. 
