CHARACTERISTICS OF INSECTS AND THEIR RELATIVES 21 



appendages of the first body-segment. These are the mandibles 

 (Fig. 29, A), which are stout and consist each of two segments; the 



maxilla (Fig. 29, B, a), which are foliaceous, 

 and usually regarded as biramous ; the second 

 maxillae or palpognaths. which are le^-like in 

 form, consisting of five or six segments, and 

 usually have the coxae united on the middle 

 line of the body (Fig. 29, B, 6), and the poison- 

 daws or toxicognaths, which are the appendages 

 of the first body-segment (Fig. 29, C). 



The poison-claws consist each of six seg- 

 ments, of which the basal one, or coxa is usually 

 fused with its fellow, the two forming a large 

 coxal plate, and the distal one is a strong pierc- 

 ing fang in which there is the opening of the 

 duct leading from a poison gland, which is in 

 the appendage. 



The legs consist typically of six segments, 

 of which the last, the tarsus, is armed with a 

 Fig. 28. A centipede, single terminal claw. The last pair of legs are 



directed backwards, and are often greatly 



modified in form. 



The class Chilopoda includes two quite distinct groups of animals 

 which are regarded by Pocock ('n) as sub-classes, the Pleuro- 

 stigma and the Not o- 



stigma. The names f^M S&.Jf'A C 



of the sub-classes 

 refer to the position 

 of the spiracles. 



SUB-CLASS 

 PLEUROSTIGMA 



The typical Centipedes 



In the typical cen- 

 tipedes, the sub-class 

 Pleurostigma, the 

 spiracles are paired 

 and are situated in the sides of the segments that bear them. Each 

 leg-bearing segment contains a distinct tergum and sternum, the 

 number of sterna never exceeding that of the terga. The eyes 



Fig. 29. Mouth-parts of a centipede, Geophilus flam- 

 dus. A, right mandible, greatly enlarged. B, the 

 two pairs of maxillae, less enlarged; a, the united 

 coxae of the maxillae; b, the united coxae of thj 

 second maxillae or palpognaths. C, the poison claws 

 or toxicognaths (After Latzel) 



