CHILOPODA 



421 



cox. 



is possibly connected with the great development of the first pair 

 of trunk appendages as maxillipeds, which are four-jointed, the 

 distal joint being a sharp claw perforated by the opening of the poison 

 gland, while the proximal joint is enlarged and meets its fellow in the 

 middle line to form an additional lower lip. 



The body segments in Lithobiiis number eighteen. Of these, the 

 ist carries the poison claws (maxillipeds), the 17th the genital opening 

 and usually a pair of modified appen- 

 dages, the gonopods, and the last 

 (telson), which is greatly reduced in 

 size and not seen in Fig. 297, the 

 anus, while the 2nd to i6th have 

 each a pair of seven-jointed walking 

 legs. Each segment has a broad 

 tergum and sternum and between 

 them a soft pleural region with a few 

 small chitinous sclerites and the stig- 

 mata. In Lithobius and the group of 

 chilopods to which it belongs, the 

 terga are alternately long and short 

 (Fig. 294). Only the segments which 

 have long sterna have stigmata, but 

 all have walking legs. In other centi- 

 pedes, e.g. Scolopendra (see Table, genital segment, 

 pp. 306-7), the terga are equal gonopods. 

 throughout. 



The alimentary canal consists of a short fore gut into which open 

 two or three pairs of salivary glands, a very long mid gut without any 

 associated glands, and a short hind gut into which open a pair of 

 Malpighian tubules. 



The vascular system is better developed than in insects. The 

 heart runs the whole length of the body and possesses in each segment 

 not only a pair of ostia but also lateral arteries. It ends anteriorly in 

 a cephalic artery and a pair of arteries which run round the gut and 

 join to form a supraneural vessel. The arteries branch and open into 

 haemocoelic spaces. There is a pericardium and below it a horizontal 

 membrane, perforated and provided with alary muscles as in insects. 

 In the respiratory system the tracheae branch and anastomose and 

 possess a spiral thickening, but in the remarkable form Scutigera the 

 stigmata are unpaired and dorsomedian in position and the tracheae 

 are unb ranched and simple in structure. 



The reproductive organs (Fig. 295) consist of an unpaired ovary or 

 testis, with a duct which divides into two and passes round the end 

 gut to open by the median genital opening. There are two pairs of 



--'g.pod. 



Fig. 297. Lithobius forficatus, ?. 

 Hind end, ventral side. 16, last 

 segment bearing ambulatory legs ; 

 cox. coxopodite of last leg; 17, pre- 

 hearing g.pod. 



