316 The Structure and Action of a Butterfly s Trunk. (May, 
hair structures in the emperor, however, are not prominent enough, 
one would think, for mechanical action, and in this and similar 
cases, their function is probably wholly that of touch or taste. 
This view is strengthened by their occurrence also wethin the tube, 
where they appear, but in lesser numbers. 
If we imbed the trunk in a mass of paraffine or soap, and cut 
some thin transverse sections, we shall obtain with the microscope 
a view of its structure as seen in Fig. 3. Each half of the trunk, 
that is, each maxilla—has a sort of moon-shaped section, the lower 
horn of which is snugly dovetailed to the lower horn of the oppo- 
site half, while the upper horns are drawn out into long processes, 
which simply interlace like the fingers of one hand with the 
other. There is thus inclosed a central canal open from base to 
tip of the trunk, and its walls are made up of broad but thin, 
semicircular pee whose narrow edges give the canal wall, seen 
from the side, much the appearance of a 
large trachea, or air-tube (Fig. 4, ¢). 
Each half of the trunk also contains a 
real air-tube (¢7, Figs. 3 and 4), a nerve 
(n) and two sets of muscles (7 and m°), 
while the rest of the space is filled out 
with connective tissues. 
It has generally been believed? that the 
j trunk is extended by muscular action, 
#-%---m being rolled up in repose by its own elas- 
ticity, like a watch-spring, but the trunk 
muscles seem, at first sight, to be ar- 
ranged for just the opposite state of 
N 
= things. They are grouped in two sets in 
= each half of the trunk, each set arising 
soe on the anterior surface, and proceeding 
oe ©, 4 — Longitudinal se sec- diagonally downward and backward to 
shown above; lower down the be inserted on the posterior surface. They 
trachea, ¢v, and the nerve, n; at, 
while the diagonal muscles, 7z, SER cher — in this course, so that, 
overlie them. These are spaced viewed from in front, the two sets of mus- 
somewhat wider than in nature, ‘ i 
for the sake of clearness. ‘The CICS frii a Jérica of V's ope above the 
right edge is the outer one? other. One of the sets is seen in the ver- 
tical section of the right maxilla (Fig. 4), and if we examine this — 
1See directions given by Dr. C. S. Minot in the NATURALIST for April, 1 
2 This is the statement of the latest text-book, that of at die Insecten, 4 I 56, 
e cross sections of the rings forming the edges of the figure engrave 
as much too irregular. The inner boundary of the cuticle i is a omitt 
