200 Wisconsin Academy of Sciences, Arts, and Letters. 
The following quotations are relative to the frenulum. Kirby 
and Spence (11), Letter XXIII: 
“The wings of many butterflies, hawk-moths, and moths are dis¬ 
tinguished by a remarkable apparatus, noticed by de Geer, and since 
by many other naturalists, for keeping them steady and underanged 
in their flight.” 
These authors also noticed the difference in the frenulum be¬ 
tween the two sexes: 
“The females, which seldom fly far, often have the bristles, but 
never the hook.” 
Comstock (4) has the following: 
“Except in the Microlepidoptera the frenulum of the male consists 
of a single strong spine, that of the female of two or more bristles.” 
From another account by Comstock (5); 
“If one of the bristles of the compound frenulum of the female be 
examined it is found to be hollow, containing a single cavity. But 
when the frenulum of a male is examined it is found to contain sev¬ 
eral small cavities. Evidently the frenulum of the male is composed 
of several bristles as is that of the female, but these bristles are 
grown together, forming a single spine.” 
One of the latest accounts of the frenulum is by Tillyard (14). 
In this work the wing-coupling apparatus of the Lepidoptera and 
of other orders of insects is discussed. 
The frenulum of the wax moth appears as a slightly curved 
bristle on the costal margin of each hind wing near the humeral 
angle. It is borne on the humeral lobe. In the male moth a 
single bristle is present on each wing; in the female there are 
generally three. There is a variation in this number in the fe¬ 
male (this will be discussed later), but at present we will assume 
that three bristles, the most regular number, are present. 
In studying the development of the frenulum, one is early im¬ 
pressed with the fact that it is similar to that of all other hairs, 
etc., on the wings and on the bodies of insects; such an out¬ 
growth is the product of a single cell, a trichogen. Very early 
in the development it is apparent that each frenular bristle of 
the female arises from a single trichogen and that it remains at 
all times separate from the others; in the male the large frenu- 
