NEREIS 



187 



iud 



related with its carnivorous life are its powerful jaws and well- 

 developed sense organs on the head. These consist of eyes, 

 feelers, and tasting organs. 



From such forms as Nereis there has developed a long series 

 of worms inhabiting the sand or constructing special tubes 

 in which to live. At the end of the 

 series there are includetl worms that live 

 permanently in thin limj^ tubes and have 

 lost the locomotor and sense organs of 

 Nereis. We shall examine in order some 

 of these different worms and shall ob- 

 serve certain modifications in structure 

 which they undergo in relation to their 

 modified life. 



But first we should know that not all 

 free-living, marine annelids are like 

 Nereis. On the one hand we have forms 

 that do not l^urrow at all in the sea 

 bottom, but which lie so close to stones 

 and shells that they seem to form a 

 part of them. Their flat body is covered 

 with scales, and they are known as Fig. 179.— Autolytus, a 



, . ., f representative of a fam- 



scaled-worms (rig. 177). In a tew 

 members of this group, known as " sea- 

 mice " (Fig. 178), the scales are hidden 

 from view by long bristles. These bris- 

 tles are merely greatly enlarged represen- 

 tatives of the bristles found on the swimming pads of Nereis. 

 A second form (Autolytus \ Fig. 179) lives in little tubes 

 attached to seaweeds and hydroids. Its method of repro- 



^ atitos, self : luo, to separate ; hence, self -separating. 



ilj' of Polychoeta in 

 which the animal l:)uds 

 off male or female in- 

 dividuals from its hinder 

 end. bud, head of the 

 budded individual. 

 After A. Agassiz. 



