238 MYRIOPODA. 



are found on the first, third, and fourth trunk-segments (Fig. 122).* Two trun- 

 cated pairs of legs lying below the integument belong to the fifth segment, and 

 another pair of the same kind to the sixth segment. After ecdysis these limbs 

 project freely, and the stage with seven segments and three pairs of legs is 

 followed by one with nine segments and six pairs of legs. The next (third) 

 stage has twelve segments and ten ( g \ or eleven ( J ) pairs of legs. The 

 sixth segment now has one instead of two pairs, and the seventh segment of 

 the female has two pairs, while in the male it carries only one. The copulatory 

 limbs of the male which lie on the seventh segment develop only in the adult. 

 The further development of segments and limbs is set forth in the following 

 table : — 



3 pairs of legs. 



6 



10 „ (<?), 11(?). 



16 „ „ 17 „ 



00 o^ 



26 27 



28 „ „ 29 „ 



o(J ,, ,, 31 ,, 



Sexual maturity is reached in the eighth stage, and is accompanied by the 

 development of the copulatory limbs which usually belong to the seventh 

 trunk-segment in the Diplopoda. A moult occurs between each stage. 



In the Julidae examined with special care by Newport in this connection, 

 the course of development was, on the whole, similar to the above. On both 

 the fifth and sixth segments the larva has two truncated pairs of legs beneath 

 the integument, which, after the first moult, appear as well-developed limbs. 

 Through later moults each of the following segments also develops two pairs of 

 legs, and the number of segments increases from before backward. 



In both the larval and the adult condition of Strongylosoma, Polydcsmus, and 

 Julus, one of the four anterior segments is without limbs, this being the second 

 segment in the first two genera, while in Julus it is the third (Figs. 121 B and 

 122). In Polyxenius this seems not to be the case ; the larva of this Diplopod 

 has at first only five trunk -segments (the anal segment included) and three pairs 

 of legs attached to the three anterior segments. In the next stage the number 

 of segments is the same, but another pair of legs appears on the fourth segment 

 (Bode). This last pair is retained as a single pair when, in the third stage, a 

 pair develops on the newly-formed fifth segment, and during the moult which 

 follows another pair is added on this last segment. During the eight stages 

 passed through by this larva, three other segments, each provided with tw r o pairs 

 of legs (the sixth, seventh, and eighth), are added, the ninth segment, however, 

 carries only one pair of limbs, while the segment lying in front of the anal 

 segment is devoid of extremities (Bode, Latzel, vom Rath). It is character- 

 istic of the terminal segment in the Diplopoda that no fusion takes place in it, 

 and this is also the case with the four anterior segments (known as the thorax), 

 and, apparently, fusion is also absent in the genital segment. 



C. Symphyla and Pauropoda. 



Up to the present time, as far as we know, nothing is known of the embryonic 

 development of these Myriopoda which, on account of their minute size, are 



* [See footnote, p. 237. — Ed.] 



