NEREIS 



185 



there. These animals of the quiet harbor are mostly weak and 

 defenceless ; they seek chiefly to avoid their enemies by retreat- 

 ing from them. Between the rocky promontories and the 

 salt-marsh exist all possible gradations, and in each different 

 habitat one will find a totally different fauna. 



In this chapter we shall consider an animal living in the 

 bottoms of harbors, laiown as the sandworm (Ne'reis). It 





S^^"; 



Fig. 176. — An estuary with a salt-marsh m the distance where semiaquatic 

 plants grow far out into the sea. 



abounds in sandy or muddy beaches at or below low-water 

 mark and is especially abundant where tidal currents flow 

 swiftlj^ thus constantly renewing the water, oxygen, and food 

 particles. Nereis is, for the most part, a lover of darkness 

 and contact. Hence it inhabits burrows which it lines with 

 a secretion of mucilaginous consistency that binds together 

 the particles of sand or mud. For a week or two in summer, 

 however, during the breeding season. Nereis gains a new set 

 of instincts. It leaves its burrows and swims about near the 

 surface of the sea. 



