TRACHEATA. 391 



fourth are each provided with a single functional pair of limbs ; 

 the fifth segment is provided with two pairs of rudimentary 

 limbs, which are involuted in a single sack and not visible with- 

 out preparation, and therefore not shewn in the figure. The 

 sixth segment is provided with but a single pair of appendages, 

 though a second pair is subsequently developed on it 1 . 



Julus, at the time it leaves the chorion, is imperfectly segmented, but is 

 provided with antennae, mandibles, and maxillae, and seven pairs of limbs, 

 of which the first three are much more developed than the remainder. 

 Segmentation soon makes its appearance, and the head becomes distinct 

 from the trunk, and on each of the three anterior trunk segments a single 

 pair of limbs is very conspicuous (MetschnikoffJ". Each of the succeeding 

 segments bears eventually two pairs of appendages. At the time when 

 the inner embryonic cuticle is cast off, the larva appears to be hexapodous, 

 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 completed. 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 



1 Though the superficially hexapodous larva of Strongylosoma and other Chilo- 

 gnatha has a striking resemblance to some larval Insects, no real comparison is pos- 

 sible between them, even on the assumption that the three functional appendages of 

 both are homologous, because Embryology clearly proves that the hexapodous Insect 

 type has originated from an ancestor with numerous appendages by the atrophy of 

 those appendages, and not from an hexapodous larval form prior to the development 

 of the full number of adult appendages. 



2 Newport states however that a pair of limbs is present on the first, second, and 

 fourth post-oral segments, but that the third segment is apodous ; and this is un- 

 doubtedly the case in the adult. 



