110 STRUCTURE OF MYRIAPODA AND ANNELIDA. 



through a series of metamorphoses, in which they lose their 

 eyes and legs, and become fixed for the remainder of their 

 lives. 



103. We now pass back to another class of the higher 

 group of Articulata, adapted to breathe air and to inhabit 

 the land, the MYRIAPODA or Centipede tribe (fig. 42). Both 

 these names are derived from the great number of legs 

 possessed by these animals, which often amount to 60 pairs 

 or even more. In. this class we see a more perfect equality 

 of the segments or divisions of the body than in any others 

 among the higher Articulata; and the similarity is scarcely 

 less complete in the internal arrangement, than it is in the 

 external form. In its lower tribes (fig. 51), the legs are so 



Fig. 51. IULUS. 



weak as scarcely to be able to sustain the body, which moves, 

 therefore, partly in the manner of that of a worm. The 

 animals of this class undergo 110 proper metamorphosis ; but 

 there is a considerable adoption to the number of their seg- 

 ments and legs after they have come forth from the egg. 



104. We now pass to the lower division of Articulata, in 

 which the body possesses no jointed members ; and the animals 

 belonging to this group are for the most part included in the 

 class of ANNELIDA, the Leech and Worm tribe. We here find 

 the body enveloped, not in a hard casing, formed of distinct 

 pieces united by a flexible membrane, but in a skin which 

 is altogether flexible, and which gives little indication of a 

 division into segments. This class includes several distinct 

 tribes, which all agree, however, in the long worm-like form 

 of the body, and in the similarity of the different ganglia 01 

 their nervous system. The Earth-worm and its allies are 

 adapted to live on land and to breathe air ; but the greater 

 number of Annelids are purely, aquatic ; and these breathe 

 by gills, which form tufts that are disposed on various parts 

 of the body. In the Nereis, or Sea-centipede (fig. 52), these 



