209 
Cicadellidae, and Fulgoroidea were well established; and one of 
the oldest fossil insects, Prosbole of the Permian, can be placed 
in the existing family Tropiduchidae. 
During the course of insect evolution a number of attempts 
have been made to produce a piercing and sucking mouth. [or 
perfection of mechanism none surpasses, nor even equals, that 
of the Hemiptera. This may account for the constancy of type 
through such a long period of time and in such a large group. 
With the exception of the Thysanoptera and Anoplura, where 
the mouth parts are much more generalized, the Hemiptera is 
the only order of ametabolus insects with a complete piercing 
and sucking mouth, and the only order in which such a type of 
mouth arises in the embryo. 
There are a number of types of venation within the order, 
but I know of no one character, or group of characters, by 
which all can be separated from all other orders. 
Tue Two SuBorDERS. 
The two suborders, the Heteroptera and the Homoptera, are 
divided mainly on the shape of the head and the position of the 
labium. In the Heteroptera there is a well-developed gula, 
which is very long in some groups; the head projects forward 
and the proboscis is bent at its base and lies under the head 
when at rest. In most of the Heteroptera there are four seg- 
ments to the labium, but in some the mentum and submentum 
are fused, thus making only three segments. In the Homoptera 
the gula is absent or represented only by a small membrane; 
the head is deflexed and inflexed so that the base of the labium 
is in intimate connection with the prosternum; the submentum 
is membraneous, and in many forms the mentum is reduced. 
The labium, when at rest, projects backward between the legs. 
more or less in line with the head, and is not bent at a sharp 
angle to it. 
Of the two suborders the head of the Heteroptera appears to 
me to represent the more generalized type. Whether the primi- 
tive Hemiptera had its mouth organs deflexed beneath its head 
or standing straight out, it is difficult to judge. The highly 
developed mouth organs of the Heteroptera of today are not the 
primitive type of the order. This was evidently a more general- 
