H YMEN OP TER A. 
021 
The Mossy Rose-gall, Rhodites rosce (Rho-di'tes ro'sEe), 
is a very common polythalamous gall, which is formed on 
the stem of the sweetbrier (Fig. 747). The gall consists of 
a large number of hard kernels surrounding the branch and 
covered with reddish or green, moss-like filaments. In each 
of these kernels a gall fly is developed. 
The Guest Gall-flies or Inquilines (In'qui-lins).—There are 
many gall-flies that do not form galls, but lay their eggs in 
the galls made by some other species. The larvae of these 
guest gall-flies feed upon these galls, and in many instances 
do not discommode the owners in the least. 
Family TrigonalidAl (Trig-o-nal'i-dae). 
The Trigonalids ( Tri-gon’ adids). 
This family includes only one genus, Trigonalys (Tri- 
gon'a-lys), of which there are only four North American 
species. All of these are rare. 
In this genus there is a distinct cell between veins I and 
III of the fore wing; the stigma is well developed ; there is 
only one marginal cell, but this reaches nearly to the apex 
of the wing; and there are four submarginal cells. 
Family ICHNEUMONIDA2 (Ich-neu-mon'i-dae). 
The Ichneumon-flies. 
When the discouraged farmer sees his crops harvested 
before due time by hordes of hungry insects, he is apt to 
long for a miracle to remove the plague from his fields. 
Oftener than he dreams the miracle takes place, and millions 
of insect pests never live to lay their eggs for another brood. 
Such miracles arc most frequently wrought by members of 
this and the allied families. These constitute a group com¬ 
monly spoken of as the Parasitic Hymenoptera (see Synop¬ 
sis, p. 601), a group containing the great majority of all 
parasitic insects. 
Very many other insects play an important part in the 
