402 



ZOOLOGY. 



or even encrusted with a calcareous epidermis, and thus is, 

 at most, a tegumentary skeleton. 



508. In certain of the articulata or annelides, as in the 

 scolopendra (Fig. 164), the rings strictly resemble each other ; 

 and this tendency to repetition is worthy of observation. 

 Each ring may carry two pairs of appendages or limbs, one 

 belonging to its dorsal arch or upper portion (Fig. 413), the 

 other to the lower or ventral ; and when these appendages 

 happen to be but little developed, all the rings are, in fact, 

 provided with limbs. But in general the appendages of cer- 

 tain rings acquire a large development, as if at the expense 

 of the others, which in this case remain rudimentary. It 

 almost always happens that it is the lower appendages which 

 are thus developed, and which assume varied forms, accord- 

 ing as the animal is higher or lower in the scale. Differently 



Dorsal Arch. Dorsal Oar, or Swimming Paw. 



Feet 



Ventral Arch. Ventral Oar or Paw. 



Fig. 413. Vertical Section of a Bing or Segment of the Body 

 of an Ann elide of the genus Amphinome. 



modified, they form the antennae, the various organs of mas- 

 tication, the feet, fins, &c. (Figs. 143, 144). Sometimes the 

 upper appendages remain and perform, like those of the 

 inferior arch, the office of feet : various annelides offer 

 examples of this; but generally they exist merely on the 

 rings situated towards the middle of the body, and they 

 constitute the wings, or organs held as analogous to them. 

 The feet are generally three, four, five, or seven pairs in 

 number, but occasionally they are in hundreds, and sometimes 

 altogether absent ; in that case, they seem to be represented 

 by coarse hair in bundles, as may be seen in earth-worms. 



