422 



THE INVERTEBRATA 



accessory glands and in the male two vesiculae seminales. Spermato- 

 phores are formed but it is doubtful whether copulation occurs. 

 Lithobius lays its eggs singly and buries them in the earth. The young 

 are hatched with seven pairs of legs. 



The nervous system comprises a cerebral ganglion supplying the 

 antennae and the eyes, a suboesophageal ganglion giving branches to 

 the other head appendages and the maxillipeds, and a ventral chain 

 with a pair of ganglia in each leg-bearing segment. 



Class DIPLOPODA 



Arthropods with the genital opening situated on the 3rd segment 

 behind the head (progoneate) ; trunk segments arranged in an anterior 

 region {thorax) of four single segments and a posterior region [abdomen) 

 of double segments, each with two pairs of legs; body usually cylin- 

 drical; skeleton strengthened by a calcareous deposit; ocelli present, 

 head bears also short club-shaped antennae, mandibles and a single 

 pair of maxillae; vascular system well developed as in Chilopoda; 

 tracheae arise in tufts from tracheal pouches, do not anastomose; 



— 1 



Fig. 298. lulus terrestris, sometimes called the "wire-worm", x about 3^, 

 From Koch, i, antennae; 2, eyes; 3, legs; 4, pores for the escape of the 

 excretion of the stink glands. 



gonads ventral to gut ; young hatch usually in a stage with three pairs 

 of legs and development takes place gradually. 



Though the head of the adult millipede appears to have fewer 

 segments than that of the Chilopoda a study of the embryo shows 

 that there are really the same number. An intercalary segment exists 

 between the antennal and mandibular segments and behind the 

 mandibles a pair of rudimentary appendages appear but soon vanish. 

 These are the first maxillae: the second maxillae (labium) persist in 

 the adult. 



lulus is one of the commonest genera of millipedes. It is vege- 

 tarian. It has an elongated body, consisting of a large number of 

 segments (up to seventy), which can be rolled into a ball. The head 

 (Fig. 299 A) carries a pair of short antennae with seven joints. The 

 labrum is continuous with the front of the head and is a toothed 

 plate; the mandibles, which have no palp, bear a movable tooth and 



