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What lies below that surface—the branches, limbs, and trunk— 
we can only speculate about, using for our guides the arrange- 
ments of fhe terminal twigs and such little evidence as is given 
us by paleontology. Such speculation we term phylogeny, and 
its existence entirely depends upon our belief in evolution; the 
form it takes is moulded by the nature of that belief. 
To the phylogenist the cut and dried dichotomous characters, 
which are such a boon to systematists, are often of little value. 
On the other hand, those organs showing a graduate series, 
which are anathema to the systematist, are generally the phy- 
logenist’s best friends. It is upon these lines that the following 
speculations proceed. 
The Hemiptera existed before the Heteroptera or Homoptera, 
and were characterized by the nature and function of the mouth 
parts. They were more generalized that either of these sub- 
orders are today, but they approached nearer to the former. 
The head would have possessed a gula region, and the beak may 
have been carried out straight. When not in use this position 
would be inconvenient, and it was possibly to avoid this that 
the main dichotomy came about. In the Heteroptera the gula 
region persisted and even became greatly developed and the 
beak bent at its base so that it packed away under the head and 
thorax. In the Homoptera the gula was reduced and the head 
became inflexed so that the beak when at rest lay straight out 
beneath the thorax without a bend at its base, thus the base of 
the labium was brought into intimate relationship with the pro- 
sternum. This turning under of the head led to a flattening and 
widening of the head capsule, especially the more apical por- 
tions such as the genae and lorae. This line of evolution of the 
head was carried to its greatest extent in the Cicadoidea, more 
especially in the specialized Cicadellidae. The Tettigometridae 
of the Fulgoroidea retains this type of head, but it is modified 
slightly along the fulgorid lines. It is possible that in the Ful- — 
goroidea the vertex lengthened and curved downward. In this 
case the lateral carinae of the frons would represent the ridge 
above the antennae in the Cicadoidea. 
After the departure of the Fulgoroidea from the main stem, 
or perhaps even before that, there arose the peculiar arrange- 
ment of the intestine whereby the “filter” or “colum” was 
