MILLIPEDES 19 



and North Africa and have a great and variable number of tergal 

 plates, most of w^hich are provided v^ith repugnatorial glands. The 

 anterior pair of legs of the seventh segment is again modified, as 

 sperm carriers how^ever, and the seminal ducts perforate the basal 

 segments of the second pair. Some species of Lysiopetalum may 

 reach four or five inches in length. 



The last order of Chilognatha is the Opisthospermophora, the 

 members of w^hich have a large and variable number of cylindrical 

 tergal plates all of which, except for a few at the anterior end, are 

 provided with repugnatorial glands. In number of species, genera 

 and families, the order surpasses all other orders of the Chilo- 

 gnatha. The families are usually grouped into three sub-orders, 

 the first of which includes the Stemmiulidae which are found in 

 the tropics of Asia, Africa and America. The second contains the 

 families lulidae, Blaniulidae, which are represented in Britain by 

 many species and genera, and the Spirostreptidae which is abun- 

 dant in the tropics and contains some of the largest millipedes in 

 the world. The third sub-order includes the Spirobolidae which 

 are also widely distributed in tropical regions and are represented 

 by numerous genera and species, some of which rival the largest 

 species of Spirostreptus in size. 



The sub-class Pselaphognatha contains a single widely dis- 

 tributed order, Penicillata, comprising the family Polyxenidae and 

 two genera Polyxenus and Lophoproctus. These are minute milli- 

 pedes having a soft integument without horny plates but richly 

 provided with rows and tufts of peculiarly shaped bristles. The 

 mouthparts are complicated and appear to consist of four pairs. 

 The body is composed of eleven somites of which the first four 

 carry a single pair of legs, the next four two pairs and the ninth one 

 pair, the last two segments being legless. Of the thirteen pairs of 

 legs none is modified as gonopods. One species, Polyxenus laguruSy 

 occurs in Great Britain. 



General behaviour 



From a study of the locomotory mechanisms and associated 

 structures of a series of millipedes representing the major sub- 

 divisions of the Diplopoda, Manton (1954) has shown that the 

 evolution of the class has been related to the development of a 



