EXTERNAL ANATOMY OF THE MOTH. 
51 
the thorax. Each of the segments consists of a dorsal, two lateral (one 
on each side) and a ventral piece. The side piece or membrane of the 
first seven segments bears a spiracle. The first segment, in its trans- 
verse diameter, is nearly as broad as the thorax, but its dorso-ventral 
diameter is barely half as great. In front it bends over and inwards, 
especially at the sides, so that here (see Plate XI, Fig. 3) the crnst, where 
it joins the thorax, faces towards the head. It is here that the spiracle 
(sj>) is placed, so that in a side view of the abdomen we see the edges 
of the spiracle, and not its opening, as in the other segments; the spir- 
acle looks forwards. 
The structure of the spiracles is interesting. They are all essentially 
alike. Plate XI, Fig. 1, represents that of the second abdominal seg- 
ment. The spiracle is a vertical fissure with two lips, of which the an- 
terior is connected with a long tendon, to which are attached the mus- 
cles which move the lips. Outside the lips is a row of stiff hairs, or 
Spines, which, standing out from the borders of the fissure, reach to- 
wards its center, so that those of the opposite sides nearly meet in the 
middle. Fig. 2 of the same plate gives a more magnified representa- 
tion of !i sin^h* spine. It rises from a pore-canal (or tube running 
through the outicola), makes a bend at the start, and then runs out 
nearly straight, a thick stem, from the outer half of which arise a num- 
ber of oblique prickles or thorns irregularly placed. The shaft consists 
of a hard sheath and a core or pulp. The hairs on the front edge are 
a little shorter than those on the posterior. At the top and bottom of 
the fissure the hairs become very small. The purpose of these spines 
is undoubtedly protective; they serve to prevent the entrance of foreign 
bodies, like the similar structures in the spiracles of the caterpillar. In 
the adult there is a single row of long spines ; in the larva several rows 
of short spines. 
The legs offer little requiring special description. The tarsal joints 
are five on each leg. After removal of the scales they are seen to be 
armed with a double row of spines on their inner margin (1*1. IX, Fig. 
2), except the last joint, which has only hairs. The spines are shortest 
on the upper part of each joint and increase towards the distal end, the 
lowest spine being the longest. The end of the last joint bears in front 
two long, curving hairs, and behind the two recurved hooks, between 
which is placed the soft hairy pad, or pulvillus, p. The other joints are 
distinguished by their gradual diminution in length, the first or upper 
being the longest and having also the largest number of spines, as well 
as the greatest intervals between the adjacent spines. The scales on 
the legs are peculiarly grouped, being inserted in little clusters of some 
10 to 15. Each cluster is very compact and elongated, in the sense of 
the long axis of the limb. 
The scales are flattened hairs, divided into a blade of variable shape 
and a short pedicel, by which they are attached to the skin. The blade 
consists of a central portion, homologous with the core of hairs, and 
