16 MILLIPEDES 



treated as a separate class. The name Diplopoda, which means 

 'double-footed', was given to them because in these animals most 

 of the segments of the body are provided with two pairs of limbs, 

 a condition arising from the confluence of two adjacent tergal 

 plates. As in the Pauropoda and Symphyla, the reproductive 

 organs have their apertures on the ventral side of the fore part of 

 the body near the head, whereas in the Chilopoda these open on 

 the last abdominal somite as they do in insects. Millipedes have a 

 distinct head bearing a pair of short, unbranched antennae, at least 

 two pairs of jaws and usually eyes. Spiracles leading into tubular 

 tracheae open above the coxae of the legs and the dorsal plates of 

 the segments are greatly developed as compared with the ventral. 

 The majority of the Diplopoda are included in the sub-class 

 Chilognatha and their integument is hard and horny. Each double 

 segment is composed typically of a vaulted or nearly circular ter- 

 gum, one or two small pleural plates, two sternites and two pairs 

 of legs. The tergites, pleurites and sternites may all be movable, 

 or they may coalesce into a solid ring, the significance of which 

 will be considered later. There are only two pairs of mouthparts; 

 the first are biting mandibles composed of two or three segments; 

 the second pair is fused to form a broad plate or gnathochilarium. 

 In the males one pair of legs is modified for mating purposes and 

 its structure is a diagnostic character in many species. 



Fig. 6. The pill-millipede Glomeris jnarginata. (After Cloudsley- 

 Thompson, 1956.) 



The order Oniscomorpha contains millipedes whose body is 

 short, broad, strongly convex above and flat below, and capable of 

 being rolled into a ball as in some woodlice. There are from 1 1 to 



