792 ARTHROPODA phylum vii 



which are never divided into fagmata ; there are two or three imirs of mouth ajijyendages , 

 and numerous pairs of legs. 



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

 as Centii^edes and Millipedes {Ghiloj^oda and Diplopoda), plus the more recently 

 established groups of Pauropoda and Symphijla, 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 Arthroj)ods as independent classes of 

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

 Ijetween the Chilopoda (Centipedes) and the Hexapoda (Insects), on the one hand, than 

 between the Chilopoda and Diplojooda on the other. According to the modern system 

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

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



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

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

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

 groujjs of which Centijiedes and Millipedes are the most important members are here 

 treated as classes, conformal)ly 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. CarjDenter, 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, Geophilus, and Apus must be regarded as a secondary 

 condition." 



Class 1. DIPLOPODA Gervais (CMo(7m«Aa Latreille). (Millipedes). 



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

 variable number (from 12 to 150), and the majority of them fused pairioise, each tergite 

 bearing two pairs of legs. Head with one pair of short, seven-jointed antennae, one pxiir 

 of mandibles, and one or two pairs of maxillae. No compound eyes, but numerous ocelli 

 usually present. 



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

 legs to each segment. The anterior pair, or both pairs of legs corresj^onding to the 



seventh tergite are usually modified as copulatory organs 

 (gonoi^ods), 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. Resj^iration 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 



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



Jalusan.tiquiM'iieydw. Upper tives, especially in amljer. Among Tertiary examj)les may 



S!G™?y^''4.^°"' "'"" l^e mentioned the following: JuUs Linn. (Fig. 1528); 



Graspedosoma Leach ; Euzonus Mewge ; Polyxenus Latreille; 



1854. — Peach, B. N., On some new Myriapods from the Palaeozoic rocks of Scotland.' Proc. Phys. 

 Soc. Edinb., 1899, vol. xiv; — Pocock, R. I., Articles on Centipedes and Millipedes in Encycl. Brit., 

 1911. — Scuddci; S. JI., On Carboniferous Myriapods. Mem. Boston Soc. Nat. Hist., 1873-90, 

 vols, ii.-iv. — Idem, Index to the known fossil Insects of the World, including Myriapods and 

 Arachnids. Bull. U.S. Geol. Surv., No. 71, 1891. — Cockerell, T. D. A., Catalogue of the generic 

 names based on American Insects and Arachnids from the Tertiary rocks, with indications of the 

 type species. Bull. Amer. Mus. Nat. Hist., 1908, 1909, vol. xxvi! 



