ANNULOSA : MYRIAPODA. 



coalescent, and have their appendages specially modified to 

 subserve prehension" (Huxley). Pauropus has only nine 

 pairs of legs ; but, with this exception, eleven 

 pairs of legs is the smallest number known in 

 the order. 



The respiratory organs, with one exception, 

 agree with those of the Inserta and of many of 

 the Arachnida in being "tracheae" that is to 

 say, tubes, which open upon the surface of the 

 body by minute apertures, or " stigmata/' and 

 the walls of which are strengthened by a spirally- 

 coiled filament of chitine. The tracheae may 

 or may not anastomose with one another as 

 they do in Insects. 



The somites, with the exception of the 

 head and the last abdominal segment, are 

 usually undistinguishable from one another, 

 and each bears a single pair of limbs. In 

 some cases, however, each segment appears to 

 be provided with two pairs of appendages 

 (fig. 103). This is really due to the coales- 

 cence of the somites in pairs, each apparent 

 segment being in reality composed of two 

 amalgamated somites. This is shown, not 

 only by the bigeminal limbs, but also by the 

 arrangement of the stigmata, which in the 

 normal forms occur on every alternate ring 

 only, whereas in these aberrant forms they are 

 found upon every ring. 



The head always bears a pair of jointed antennae, resembling 

 those of many Insects, and behind the antennae there is gene- 

 rally a variable number of simple sessile eyes. In one species 

 (Scutigera) compound facetted eyes are present ; and in Pauro- 

 pus the antennae are bifid, and carry many-jointed appendages, 

 thus differing wholly from the antennae of Insects, and pre- 

 senting a decided approximation to the Crustacea. 



The young in some cases, on escaping from the egg, possess 

 nearly all the characters of the parents, except that the number 

 of somites, and consequently of limbs, is always less, and in- 

 creases at every change of skin (" moult " or " ecdysis "). In 

 most cases, there is a species of metamorphosis, the embryo 

 being at first either devoid of locomotive appendages, or pos- 

 sessed of no more than three pairs of legs, thus resembling the 

 true hexapod Insects. It is believed, however, that the legs of 

 these hexapod larvae do not correspond homologically with the 



Fig. 102. Centipede 

 (Scolopendra) . 



