64 BULLETIN 826, IT. S. DEPABTMENT OF AGRICULTURE. 
large wax reservoir. The structure of the cornicles themselves in this 
subfamily is essentially the same in all genera where they are present. 
In a large number of genera., however, the wax reservoir is absent 
and in some specialized tribes the cornicles are likewise absent. It is 
interesting to note that in some genera, though absent in the stem 
mother, they are present in the alate forms. 
The habit of gall formation is not found equally hi all genera 
and it would seem that those forms which have become associated 
with ants have not developed this habit to the same extent as have 
some of the other groups. However, it must be borne in mind that our 
knowledge concerning the species associated with ants is very incom- 
plete, and the writer is convinced that many of the Prociphilini will 
be found during their summer generations in this relation. Many 
of the forms cause true galls which are the result of outgrowths 
of the plant and which completely enclose the insects. Sometimes 
the stem mother lives in a gall by herself while in other cases the 
following generations live with her. The original spring gall is usually 
the result of the activities of the young stem mother. Certain species 
do not produce true galls but form pseudogalls which are due to the 
rolling or crumpling of the leaves on which the insects feed. Other 
species, again, especially during then- summer generations, feed on the 
twigs or roots of plants and give rise to excrescences by their 
feeding. It often happens that species which in their spring forms 
are gall makers, attack plants in this way in then summer generations. 
Others live on the foots of grasses during these generations and do 
not cause the excrescences produced by those species feeding on trees 
and woody shrubs. 
The association with ants is highly developed by one tribe of this 
subfamily, although all of the other tribes are to a degree tended by 
these insects. The species of the Fordini live exclusively in the nests 
of ants or are tended by them, and they are cared for very carefully 
hi return for the honeydew excreted. Ants also attend species which 
have aerial feeding habits and they may be seen carrying the root 
generations of species of Eriosoma from one place to another and 
even distributing them about on the trees. Indeed the writer once 
took advantage of the presence of ants to infest some apple seed- 
lings. A vial of apterous insects was emptied at the base of each 
tree and the ants soon could be seen running about carrying the 
aphids to suitable positions on the trees. Sometimes, however, they 
carried them away. 
