318 The Structure and Action of a Butterfly’s Trunk. (May, 
cesophagus (ve) is-seen entering it from above and behind. From 
the palate, just above the origin of the trunk, projects a triangular 
muscular flap, which we may call the oral valve (Fig. 5, ov) as it 
_ serves to close the mouth. 
The floor of the mouth is made of a thick chitinized crust, 
with a longitudinal fur- 
row between two con- 
vex regions; the floor 
thus somewhat resem- 
vexity is dotted over 
with minute transpa- 
rent papilla, which are, 
in general, similar to the 
papille already de- 
scribed, on the surface 
of the trunk. It seems 
highly natural to regard 
Fic. 6.— Rasen view of the bottom of the head, the pap illæ, in this sit- 
the top having been cut away, showing in the mid- uation at least, as taste 
J e ma a Sal te hace pa, TEANS, but T have not 
lm; cl, clypeus; an cornea of the compound eye succeeded in recogniz- 
(the left eye is not drawn); oe, cesophagus; pm, ; : Š 
one of the large muscles which move the labial 108 their ee 
palp. nection, 
The palate of the mouth, unlike the floor, is lined with a deli- 
cate membrane. The suspensory muscles of the oral sack pierce 
the muscular wall of the latter and reach the palatal membrane. 
Their contraction would evidently draw the palate away from the 
floor of the mouth, thus enlarging its cavity. At the base of the 
trunk, on its lower surface, the common duct (s d) of the two lat- 
eral salivary glands opens as is shown in Fig. 5 
From the anatomy of these parts we may understand that the 
butterfly obtains its food in the following manner: The trunk is 
unrolled and inserted in the nectary of a flower; at this moment 
the muscles which suspend the oral sack contract, and the mouth 
cavity is thus extended, creating a vacuum which must be sup- 
plied by a flow of honey through the trunk into the mouth. 
When the mouth is full the muscular sack contracts, the oral 
valve closes the aperture to the trunk and the honey is forced 
