792 / ARTHROPODA phylum vii 



which are'ne/er divided into tagmata ; there are two or three pairs of mouth appendages, 

 and num^röus pairs of legs. 



The time-honoured division of Myriapods into the Orders commonly known 

 as Centipedes and Millipedes {Ghüopoda and Diplopoda), plus the inore recently 

 established groups of Pauropoda and Symphyla, which latter have no fossil repre- 

 sentatives, has of late years been abandoned. The prevailing modern view is to 

 regard the above-mentioned groups of tracheate Arthropods as independent classes of 

 the phylum ; and the reason for this is found in the recognition of closer affinities 

 between the Chilopoda (Centipedes) and the Hexapoda (Insects), on the one band, than 

 between the Chilopoda and Diplopoda on the other. According to the modern System 

 the older fossil Millipedes, which are embraced in the extinct orders Protosyngnatha 

 and Archipolypoda of Scudder, fall within the liniits of the class Diplopoda. 



For practical purposes, however, it will be convenient to retain the designation 

 Myriapoda in a general sense, it being a familiär term, and the number of fossil 

 forms with which the paleontologist has to deal being comparatively limited. The 

 groups of which Centipedes and Millipedes are the most important members are here 

 treated as classes, conformably to the view which assigns them equal rank with the 

 exclusively Recent Pauropoda and Symphyla. Among the latter, certain genera 

 agree exactly in the numerical segmentation of the body with an isopod, a thysanuran, 

 and a primitive arachnid. This would lead to the inference, as pointed out by 

 G. H. Carpenter, that " all the Arthropodan classes must be derived from ancestors 

 with a definite number of segments, and the development of a large number of 

 somites in such forms as Julus, Geophüus, and Äpus must be regarded as a secondary 

 condition." 



Olass 1. DIPLOPODA Gervais (Chilognatha Latreille). (Millipedes). 



Trunk homonomously segmented, segments usually numerous and not ßattened, of a 

 variable numher {from 12 to 150), and the majorüy of them fused pairivise, each tergite 

 hearing two pairs of legs. Read with one pair of short, seven-jointed antennae, one pair 

 of mandihles, and one or two pairs of maxillae. No Compound eyes, hut numerous ocelli 

 usually present. 



The anterior three or four segments of the soma are free, with a single pair of 

 legs to each segraent. The anterior pair, or both pairs of legs corresponding to the 

 seventh tergite are usually modified as copulatory organs 

 (gonopods), but in one order (Oniscomorpha) it is the 

 posterior pair of legs that is thus modified. A pair of 

 genital openings is present at the base of the legs of the 

 second segment. Respiration takes place by means of either 

 tufted or tube-like tracheae with spiracles at the base of 

 the legs. 



Recent Diplopoda are divided into eight Orders. At 

 Fig. 1528. least five of the modern families have Tertiary representa- 



0ÄnTl?S7tVE t^''' '^P'^^'^^y ''' ^^^^^- ^^^^«i^g Tertiary examples may 

 Bonn, Germany. i/j. be mentioned the foUowing : Julus Linn. (Fig. 1528); 

 _^^Gmspedmoma Leach ; Euzonus Menge ; Polyxenus Latreille i 



Sof kTi^rlsgg Toi ^;.f"^y^«^ Myriapods from the Palaeozoic rocks of ScTtlaml. Proc. Phys. 

 iTu-t^dder S^^^^^^^^^^ ^., Articles on Centipedes and Millipedes in Encycl. Brit, 



loKu^iT inn'/n^^^^^^ ^''^'- ^^^^on Soc. Nat. Hist., 1873-90 



nanies ba.sed on American Insect7;;n7Araclmfd. f~ .t''f ' J' ^' '^•' ^"^'^'^^^^ "^" ^^' ^''''''' 

 type species. Bull. Amer. U^Cmllm^^^ "^■'^'- ^'''' ^"''^^'^°"^ '' '^^ 



I 



