120 
Guide to Myriopoda. 
Table-case 
No. 27. 
MYRIOPODA. 
The classes which are included together under the name 
Myriopoda are divided into two main divisions : The first of these 
contains the forms in which the genital aperture is situated in the 
anterior part of the body (Diplopoda, Pauropoda, and Symphyla). 
The second division contains the Ohilopoda, in which the genital 
aperture is situated at the posterior end of the body near the anus, 
as in the insects. 
Owing to the importance attached to this character, some 
authorities do not recognise the Myriopoda as a natural group. 
Class 5.— DIPLOPODA (Millipedes). 
The Diplopoda are terrestrial Arthropoda, which breathe 
atmospheric air by means of tracheal tubes. The body- seg- 
ments are numerous and, except at the anterior end of the 
body, each bears two pairs of legs (whence the name of the 
class), probably owing to the coalescence of adjacent segments in 
the course of development. The genital orifice is situated in the 
anterior part of the body between the second and third segments 
of the body. The head bears a pair of antennae. In the 
Chilognatha the mouth-parts consist of a pair of jointed 
mandibles, and a single quadrate plate, the “ gnctthochilarium,” 
probably representing two pairs of maxillae. In the Pselapho- 
gnatha, however, the mandibles are followed by a pair of 
maxillulae, a pair of maxillae, and a labium, the latter probably 
representing a second pair of maxillae. 
The Diplopoda are all plant feeders, and none of them are 
venomous. On the other hand, many of them possess stink- 
glands, placed along the sides of the body, which secrete an 
offensively smelling fluid. With the exception of the Pselapho- 
gnatha they are slow-moving forms. There are two sub-classes. 
Sub-class I. -PSELAPHOGNATHA. 
The members of this sub-class are small, soft-bodied forms, in 
which the body is composed of eleven segments and bears 
thirteen pairs of legs. The upper surface of the head and body- 
segments is furnished with a number of flattened scale-like hairs, 
