DIPLOPODA 381 



basilar plate. The tergite of this segment, however, forms what is ap- 

 parently the first segment after the head. This is known as the collum ; 

 though the first pair of legs appears to belong to it there are no 

 separate appendages and no stigmata. The next three have a single 

 pair of ambulatory legs apiece, a pair of ganglia and a pair of stigmata, 

 and in the embryo a pair of coelomic sacs. These four segments may 

 be said to constitute the thorax, though, as related above, the first 

 takes part in the formation of a head structure. The genital openings 

 are situated in the basal joint of the second pair of legs, which appear 

 to arise from the 2nd segment, but really belong to the 3rd. 



Behind this is the abdomen consisting of an indefinite number of 

 double segments (up to a hundred in lulus). The exoskeleton of a 

 body segment consists of a tergum and two sterna. In the double 

 segment of lulus (Fig. 285 B) the sclerites of two segments are fused 

 together to make a continuous ring. The sterna carry two pairs of 

 stigmata and legs. In the embryo there are two pairs of coelomic 

 sacs; there are two ostia in the heart and two pairs of ganglia. In 

 lulus the sterna are much shorter than the terga and also much 

 narrower so that the legs come off very close together ; also the terga 

 are narrower in front so that they can be telescoped into the terga in 

 front. The diagram here given (Fig. 285 D) shows that this relation 

 occurs when the diplopod body is straightened out ; when the animal 

 rolls up the adjacent rings are completely disengaged. 



The stigmata are elongated slits, which can be closed by a valve, 

 and they communicate with a tracheal pocket from which spring two 

 thick bunches of unbranched tracheae. These are of two sorts: 

 one long and slender, the other shorter and thicker with a spiral 

 lining. In other millipedes (Glomeris) the tracheae may become much 

 longer and branch but they never anastomose. 



The circulatory system is in a stage of development closely com- 

 parable with that of the insects. The alimentary canal bears a pair of 

 long Malpighian tubules arising from the hind gut. 



The legs consist of the same elements as in the insect, but the 

 tarsus is divided into three joints, the last of which carries a claw. In 

 the male the first leg is modified for copulation and in the yth segment 

 there is an auxiliary copulatory apparatus, consisting of processes 

 used for transferring sperm into the vagina of the female. These 

 processes may occur together with legs and so are not homologous 

 with them. There are no similar organs in the female. The generative 

 glands are unpaired with ducts opening on the 3rd body segment. The 

 eggs are yolked and are laid after copulation in a nest made of hard 

 earth. The mother keeps watch over them before hatching. 



