324 



CHTLOPODA. 



like the young Strongylosoma, but there are in reality four pairs of rudi- 

 mentary appendages behind the three functional pairs. The latter only 

 appear on the surface after the first post-embryonic ecdysis. Pauropus 

 (Lubbock) is hexapodous in a young stage. At the next moult two pairs 

 of appendages are added, and subsequently one pair at each moult. 



There appear to be eight post-oral segments in Julus at the time 

 of hatching. According to Newport fresh segments are added in 

 post-embryonic life by successive budding from a blastema between 

 the penultimate segment and that in front of it. They arise in 

 batches of six at the successive ecdyses, till the full number is com- 

 pleted. A functional, though not a real hexapodous condition, 

 appears to be characteristic of Chilognatha generally at the time of 

 hatching. 



The most interesting anatomical feature of the Chilognatha is the 

 double character of their segments, the feet (except the first three or 

 four, or more), the circulatory, the respiratory, and the nervous 

 systems shewing this peculiarity. Newport's and Metschnikoff's 

 observations have not thrown as much light on the nature of the 

 double segments as might have been hoped, but it appears probable 

 that they have not originated from a fusion of two primitively distinct 

 segments, but from a later imperfect division of each of the 

 primitive segments into two, and the supply to each of the divisions 

 of a primitive segment of a complete set of organs. 



Chilopoda. Up to the present time the development of only one 

 type of Chilopoda, viz. that of Geophilus, has been worked out. Most 

 forms lay their eggs, but Scolopendra is viviparous. The segmenta- 

 tion appears to resemble that in the Chilognatha, and at its close 

 there is present a blastoderm surrounding a central mass of yolk 

 cells. A ventral thickening of the blastoderm is soon formed. It 

 becomes divided into numerous segments, which continue to be 



FIG. 175. Two STAGES IN THE DEVELOPMENT OF GEOPHILTJS. 

 (After Metschnikoff.) 



A. Side-view of embryo at the stage when the segments are beginning to be formed. 



B. Later stage after the appendages have become established. 



at. antenna?; an.i. proctodaenm. 



