Symphyla — Chilopoda 365 



of limb-bearing body-segments is fourteen, as in our 

 supposed primitive insect. The legs on the first nine 

 abdominal segments, which in the Thysanura are 

 vestigial, and in other insects absent, are retained 

 in the Symphyla ; then come a pair of reduced limbs 

 with sense-organs, while the hindmost appendages are 

 conical, unjointed cercopods with silk-glands opening 

 at their tips (fig. 179). These frail creatures, there- 

 fore, give a fair idea of the progenitors of insects ; 

 their structure seems to indicate that the second 

 head-appendages had disappeared before 

 the abdominal limbs began to shorten, 

 and the distinction between thorax and 

 hind-body to appear. The most marked 

 feature wherein they differ from Insects 

 is the forward position of the genital 

 opening which is beneath the fourth 

 body-segment in both sexes (206, 207). 



Chilopoda. — The true Centipedes 

 (Chilopoda) also present several points 

 of affinity with Insects. The head of a 

 centipede bears a pair of feelers, a pair 

 of mandibles, and two pairs of maxilla? ; Fig. ^^q. — Scolo- 



d.i r ..• • 1 J „ fiendrcUa im- 



the presence of vestigial appendages ,„acuiata.'^itvj^. 



in the embryo between feelers and man- Magnified 6 



1. ... |.i times. After 



dibles brings the primitive chilopod head Latzei, "Die 



, .11 r \ Mvriopoden." 



into correspondence with that of the 

 primitive insect (210, 217). The position and form 

 of these vanished appendages in the developing centi- 

 pede suggests that they were a second pair of feelers. 

 The limbs of the first body-segment in a centipede 

 are modified into powerful poison-jaws for seizing 

 prey, and there follow at least fifteen pairs of leg- 

 bearing segments, and sometimes more than a hundred 

 and fifty. The extreme variation of the number of 

 body-segments in centipedes shows that this character 



