MILLIPEDES. 
209 
other are comparatively trifling, and that the present group is much less closely 
related to the insects than are the centipedes. In addition to certain anatomical 
features, millipedes differ from centipedes in the following points. They have only 
two pairs of jaws, namely, the mandibles—which are usually three-jointed—and the 
maxillae, which unite to form a large plate or gnathochilarium, acting as a lower 
lip. Besides these two pairs of appendages, the head is furnished usually with two 
clusters of eyes, and always with a pair of short antennae, never composed of 
more than eight segments, and usually of seven. The body consists as in the 
centipedes of a varying, often large, number of segments, some of which are 
furnished with two pairs of legs, and thus represent two primitive segments fused 
together. These segments are usually cylindrical in section, and although each 
a Sumatran millipede, Platyrrhachus mirandns (uat. size). 
may consist of as many as five skeletal pieces, these are frequently fused together 
to form a single horny ring. The sternal surface, or the area between the bases of 
the legs, is generally reduced to a narrow strip, the legs being almost or quite in 
contact in the middle of the lower surface. The stigmata or breathing apertures 
are placed close to the base of the limbs on their outer side; and in addition to 
these apertures, there is often a pair of orifices in each segment (except the last 
and the first four) giving exit to an odorous fluid which serves as a protection to 
its possessors. The legs are short and generally composed of 
six segments, tipped with a single terminal claw. The last 
segment is devoid of appendages, and furnished with a pair 
of movable flaps or doors, closing over the hinder end of the 
alimentary canal. 
Millipedes are divided into two subclasses, Pselaphognatha 
and Chilognatha. The former, with the single family Poly- 
xenidce, contains minute, rather soft-bodied forms, only about 
one-tenth of an inch in length, in which the body is composed 
of nine segments and bears thirteen pairs of legs. The head 
and dorsal plates are furnished with transverse rows of 
remarkably formed somewhat scale-like hairs, and there is a 
great tuft of similar hairs upon the sides of each segment, 
while the last joint is furnished with a backwardlv projecting 
tubular brush of straight bristles. The antennae are eight-jointed, and there are no 
thick glands. These minute creatures live beneath stones or the bark of trees. A 
species of the typical Polyxenus is shown in the illustration. In the Chilognatha 
VOL. vi. —14 
BRISTLY MILLIPEDE, 
Polyxenus (enlarged). 
