ANNULOSA : MYRIAPODA. 



329 



with two pairs of appendages (fig. 171). This is really due to 

 the coalescence 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 an- 

 tennae, resembling those of many Insects, and 

 behind the antennae there is generally a vari- 

 able number of simple sessile eyes. In one 

 species (Scutigera) compound faceted eyes are 

 present; and in Pauropus the antennae are 

 bifid, and carry many-jointed appendages, thus 

 differing wholly from the antennae of Insects, 

 and presenting a decided approximation to 

 those of 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 

 increases at every change of skin ("moult" or 

 " ecdysis "). In most cases, however, there is 

 a species of metamorphosis, the embryo being 

 at first either devoid of locomotive append- 

 ages, or possessed of no more than three pairs 

 of legs, thus resembling the true hexapod In- 

 sects. It is believed, however, that the legs of 

 these hexapod larvae do not correspond homo- 

 logically with the three pairs of legs proper to 

 adult Insects. In these cases the number of legs proper to 

 the adult is not obtained until after several moults, the entire 

 process being stated to occupy in some species as much as two 

 years, before maturity is reached. 



The Myriapoda are divided into three orders viz., the Chi- 

 lopoda, the Chilognatha, and the Pauropoda, to which a fourth, 

 under the name of Onychophora, must be provisionally added 

 for the reception of the genus Peripatus. 



ORDER I. CHILOPODA. This order comprises the well- 

 known carnivorous Centipedes and their allies, and is charac- 

 terised by the number of legs being rarely indefinitely great 

 (usually from 15 to 20 pairs), by the composition of the an- 

 tennae out of not less than 14 joints (14 to -40 or more), and 

 by the structure of the masticating organs. These consist of 



Fig. 170. Centipede 

 (Scolopendra). 



