Zt1 
That the Homopterous head has departed further from the 
primitive type than the Heteropterous, or is more highly spe- 
cialized, is the conclusion I have arrived at after a fairly exten- 
sive study; and that the Sternorhynchi have specialized along 
this line further than the Auchenorhynchi is a conclusion that 
appears to follow as a natural sequence. 
THE STERNORHYNCHI. 
It is beyond the scope of this paper to enter into a discussion 
of the four families, or superfamilies, forming this group. That 
they are highly specialized in habit and structure, and that the 
latter is often specialization by reduction, soon becomes evident 
to the student. The one or two jointed tarsi, the reduction of 
venation, the simplification of the genitalia, and the reduction 
of head and thorax are all characters in question. To a certain 
extent these reductions of organs coincide with reduction of size 
and a sedentary habit. From my present knowledge I am, con- 
vinced that these simplifications are specialization by reduction 
and not primitive conditions. It should be realized that ideas on 
this point are of importance, as they influence the whole con- 
ception of the evolution of the order. 
The Psyllidae, as we know them today, are too highly spe- 
cialized to form the ancestor of the other three families. This 
ancestor must either have been a much more generalized psyllid 
or a generalized aphid. The Coccidae are the extreme speciali- 
zation of the group. 
The four families, or superfamilies, that compose this group 
have been treated as suborders, and there is a tendency even to 
consider them as orders. When we examine the characters that 
are used to separate them it is found that they are very slender 
and not of sufficient weight to justify us in so doing. 
MacGillivray? divides the order into three suborders, viz., 
Heteroptera, Homoptera, and Gularostria. He restricts the term 
Homoptera to the Auchenorhynchi, and the Sternorhynchi he 
terms Gularostria. The former he defines as follows: 
“b. Antennae minute and inconspicuous, setiform or awl- 
shape; tarsi with three segments; prothorax large and con- 
FDIC GTS. eee eee a) a ee Homoptera.” 

-1 MacGillivray, 1921. The Coccidae, p. 4. 
