Marshall—Development of the Frenulum of the Wax Moth. 201 
lum is formed from at least a dozen trichogens, in a group adja¬ 
cent to each other, the bristles from which, at first separate, soon 
unite into a single piece. 
A section through a hind wing soon after it has emerged from 
the peripodial cavity will show that over the entire surface there 
is a regular unicellular layer of hypodermal cells even on that 
part where the frenulum later develops. As the wing becomes 
slightly larger, one finds in this same area that certain of' these 
hypodermal cells are larger than the surrounding ones and that 
they soon sink below the surface, a position they continue to oc¬ 
cupy. At a slightly later stage it is noticed that the wings ex¬ 
amined can be divided into two groups: in one group there are 
but three of these enlarged trichogens in each wing, in the other 
there are a dozen or more of them grouped closely together. It 
is also apparent that where there are but three of these tricho¬ 
gens present they are individually larger than in those wings in 
which there is a greater number. This difference in the size and 
number of these trichogens makes it possible to distinguish the 
female from the male moths. As this difference in size, as well 
as in the final development, is quite noticeable in the two sexes, 
each one will be treated separately. Figures 2 and 4 (Plate I) 
are drawn at about the same magnification from a male and a 
female specimen and show, at about the same age, the relative 
size of the trichogens in the two sexes. 
Male moth. When the wing has reached about one fourth to one 
fifth its normal size, there can be seen along the costal margin 
near the humeral angle a group of enlarged hypodermal cells. 
Sections show that these cells and their nuclei have, from their 
enlarged size, become very distinct and that they have pushed in 
from the surface of the wing. As yet the surface at this place 
shows only a slight elevation above the surrounding area. As 
development goes on, these enlarged cells (trichogens), become 
more clearly defined and form a group of cells each one of which 
lies close to the others. Early in their development there ap¬ 
pears from the free end of each trichogen a small, thin, papilla¬ 
like outgrowth; these at first protrude at right angles to the 
margin of the wing, but they soon bend to point towards its 
apex, thus taking up the position the frenulum occupies in the 
mature moth. At first each small outgrowth remains separate 
from all the others; soon their distal ends come in contact with 
