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 

 multislriatus ? 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- 

 deumidee, Lysiopetalidee, 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- l 

 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 



FIG. 11. Sixth pair of legs of 



Poiywnium grni<tnh<it,u," 9 : 



c*. ventral sacs; cox, coxa: **, 

 sternal plate; V Bplracle.- 



1 Morphology and classification of the Pauropoda ; also American Naturalist, 1W7. 

 p. 410. 



