600 



ZOOLOGY 



SECT. 



OKDER 1. CHILOPODA (SYNGNATHA). 



Opisthogoneata with numerous (15 173) trunk-segments, each 

 bearing a single pair of legs. Numerous tracheae opening in pairs 

 of stigmata on the sides of a number of the segments. Four pairs 

 of jaws, including a pair of poison-jaws. Feet with a single claw. 



This order includes the Centipedes (Fig. 494) and Scutigera. 



GENERAL ORGANISATION. 



External Features. The head in the Myriapoda is as well 

 marked off as in an Insect ; it appears to be composed of about 

 four fused segments. The antennae consist sometimes of many, 

 sometimes of comparatively few segments ; in Pauropus they are 

 branched. A pair of eyes, situated on the dorsal surface of the 

 head, consist of aggregations of ocelli except in 

 Scutigera, in which there are compound eyes, 

 differing, however, in their structure from those 

 of Insects. There are a movable labrum, a pair of 

 mandibles, and two pairs of maxillce. The 

 mandibles have no palps ; one or both pairs of 

 maxillae usually possess palps ; the second pair 

 of maxillae are in some groups more or less 

 united together. In the Chilopoda the first pair 

 of legs of the trunk are specially modified to 

 act as poison-jaws (maxillipedes), by means of 

 which the Centipede inflicts its poisonous bite. 



The number of segments in the body varies 

 from 10 to 173. In the Millipedes the dorsal 

 walls of the segments are very strongly arched ; 

 in the Centipedes the segments are all dorso- 

 ventrally compressed, with distinct tergal and 



Leuckart, after Lat- sternal shields separated laterally by intervals of 

 comparatively soft skin on which the stigmata 

 open. In the Chilopoda each segment bears a pair of jointed 

 legs ; of these the most anterior pair is extended forwards, 

 as already stated, to form a pair of poison-jaws (maxillipedes), at 

 the extremity of the pointed terminal joint of which opens the 

 duct of a poison-gland. In the Diplopoda each segment behind 

 the fourth or fifth bears two pairs of legs, the four or five most 

 anterior having only one pair each. In most of the Diplopoda 

 the appendages of the seventh segment are modified in the male 

 to form copulatory organs. 



The integument and body-wall do not differ widely from 

 those of Insects (see p. 621). The exoskeleton is a thickened 

 chitinous cuticle which is calcified in Diplopoda. Odoriferous 

 glands are present in most Diplopoda on some of the body- 

 segments, and open on the dorsal surface. Scolopendrella possesses 

 spinning glands. 



