1880.] The Structure and Action of a Butterfly's Trunk. 317 
figure, it would seem that by the contraction of the muscles, the 
posterior side of the trunk is pulled upwards, and of course 
shortened, and the shortening taking place along the whole side, 
the result would be the spiral rolling up of the trunk, with the 
posterior side within the coil. These diagonal muscles are the 
only ones to be found, and Newport certainly errs in speaking of 
annular muscles. On the view of the muscular action just taken, 
it is evident that the trunk must be unrolled and extended by its 
own elasticity, and not the reverse, a theory which is certainly 
very questionable, but at present I am unable to offer a better, and 
must leave the point to the decision of future investigators. Cer- 
tainly no writer I have 
found has thrown the 
least light upon the sub- 
ject, or even given a cor- 
rect general description 
of the muscular arrange- 
ment. 
At the base of the 
trunk large muscular 
bands run into it from the 
head in a diagonally op- 
posite direction to the 
trunk muscles, and are 
inserted on the anterior 
surface. Their contrac- ke 
tion of course pulls the Fie —Longitudinal section though the hend 
whole trunk-coil closely foie Ratti ravens, te as ai 
up under the head. ca m fl, floor of the aes showing arel “ 
Following now the the papili man dct dk gk 
trunk canal upwards into dona yoh =- — muscles which hold the (oe: 
the interior of the butter- 52K i its pos 
fly’s head, we find (Fig. 5) that it ends in what we may here call a 
mouth cavity, which is laterally expanded, but has no great 
diameter from front to back, that is, from palate to floor. The 
mouth cavity lies in a muscular sack (Fig. 6, seen from above), 
which is suspended within the head by five muscles, a lateral 
pair (4m), a dorsal pair (dm) and one frontal (fm). This 
oral sack is composed of muscular fibres running in a variety 
of directions as will be seen in Fig. 5; Fig. 6 shows the exterior 
appearance of the organ and its suspending muscles; the slender le 
