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TEXT-BOOK OF ENTOMOLOGY 



adult life diplopods (Julus) have a single pair of limbs on the three 

 first segments, or those corresponding to the thoracic segments of 



insects, the succeeding segments 

 having two pairs to each seg- 

 ment. 



Sinclair (Heathcote) regards each 

 double segment in the. diplopods as not 

 two original segments fused together, 

 nor a single segment bearing two pairs 

 of legs, but as " two complete segments 

 perfect in all particulars, but united by 

 a large dorsal plate which was origi- 

 nally two plates which have been fused 

 together." (Myriopods, 1895, p. 71.) 

 That the segments were primitively 

 separate is shown, he adds, by the 

 double nature of the circulatory sys- 

 tem, the nerve cord, and the first traces 

 of segmentation in the mesoblast. 

 Kenyon believes that from the con- 

 ditions in pauropods, Lithobius, etc., 

 there are indications of alternate plates 

 (not segments) having disappeared, 

 and of the remaining plates overgrow- 

 ing the segments behind them, so as 

 to give rise to the anomalous double 

 segments. 1 



FIG. 10. Freshly hatched larva of Julus 

 multistriatus ? 3 mm. long: a, 5 pairs of rudi- 

 mentary legs, one pair to a segment. 



Diplopods are also provided 

 with eversible coxal sacs, in 

 position like those of Symphyla and Synaptera; Meinert, Latzel, 

 and also Haase having detected them in several species of Chor- 

 deumidse, Lysiopetalidae, and Polyzonidse 

 (Fig. 11). In Lysiopetalum anceps these 

 blood-gills occur in both sexes between the 

 coxae of the third to sixteenth pair of limbs. 

 In the Diplopods the blood-gills appear to 

 be more or less permanently everted, while 

 in Scolopendrella they are usually retracted 

 within the body (Fig. 15, eg). 



Diplopods also differ externally from in- 

 sects in the genital armature, a complicated apparatus of male 

 claspers and hooks apparently arising from the sternum of the sixth 

 segment and being the modified seventh pair of legs. In myriopods 



i Morphology and class! ficatioii of the Pauropoda ; also American Naturalist, 1897, 

 p. 410. 



FIG. 11. Sixth pair of legs of 

 Poli/eoninm gemnaniciMn, 9 : 

 c.v, ventral sacs; cn.r, coxa; xt, 

 sternal plate; .v, spirade. 

 After Haase. 



