120 Guide to J\[yriopoda. 



MYRIOPODA. 



Table-case Tlie classes which are inchided together under the name 

 No. 27. 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 hody (Diplopoda, Pauropoda, and Symphyla). 

 The second division contains the Chilopoda, in which the genital 

 aperture is situated at the posterior end of the hody 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 

 Chilognatlia the mouth-parts consist of a pair of jointed 

 mandibles, and a single quadrate plate, the " gnathochilariitm," 

 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 meml)ers of this sub-class arc 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. 



