366 ZOOLOGY. 



acolopendra (Fig. 141), 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. 335), 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, according 

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

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

 Dorsal Arch. Dorsal Oar, or Swimming Paw. 



! 



- Cirrhi. 



~>^ S / \"5^ J*^ 



Feet. 



I 

 Ventral Arch. Ventral Oar or Paw. 



Fig. 335. Vertical Section of a Ring or Segment of the Body 

 of an Annelide of the genus Amphiuome. 



tication,the feet, fins,&c. (Figs. 122, 123). 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 (pattes) are generallj* 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 hairs in bundles, as 

 may be seen in earth-worms. 



509. The tendency to repetition, so remarkable in t In- 

 tegumentary skeleton of the annelides, extends to the muscles. 

 nervous system, and others. In general each segment li;is n 

 pair of nervous ganglions; all these are united to each other 



