168 



Annelida. 



much deeper than the others. Very frequently the two parapodia of 

 the same side are confluent, either for their whole length, or only 



Fig. 131. 



Fig. 132. 



Fig. 131. Diagrammatical section through the skiu of » Chsetopod. c ontiole, ep 

 epidermis, ep' epidermal cell, which secretes the chseta, b, m muscle-sheath, m' muscle 

 of the lower end of the ohsBta-sac. — Orig. 



Fig. 132. Anterior end of a Chaetopod (diagrammatic), h prostomiam, m oral segment, 

 with c the oral tentacles ; e the next segment. — Orig. 



at the base, so that there appears to be only one on each side, 

 but each has still its own bundle of ch^tse and its own aciculum. In 

 other cases, the upper parapodium is rudimentary or entirely absent. 

 The parapodia may be lobed, large, and well-developed ; or they 



D 



Fig. 133. Diagrammatic sections of different Chsetopods. In B the two parapodia 

 are confluent, in the notopodium (with the exception of the cirrus) is rudimentary, in D 

 (Earth-worm) the parapodia are represented only by two bristles. u, aciculum, g giU, 

 c dorsal, c' ventral cirrus.— Orig. 



are quite insignificant processes of the skin, or are merely repre- 

 sented by their chaetse, which then are planted directly in the 



