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 sumatean millipede, Platyrrhachus mirandus (nat. 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 backwardly 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). 



