CHAPTER XI 



NATURAL HISTORY OF POLYCHAETES GENERAL HABITS CHA] 



ACTER OF TUBE AND ITS FORMATION COLOURING PROTE( 



TIVE AND MIMETIC DEVICES PHOSPHORESCENCE FOOD- 



USES ASSOCIATED WORMS WORMS AS HOSTS DISTRIB1 



TION FOSSIL REMAINS. 



All the many hundreds of species of Polychaetes are marine, 

 with a very few exceptions, which have been in recent years 

 recorded from fresh {i.e. drinkable) water, viz. a species of Nereis 

 from a lake in Mingrelia, another Nereis and a Lumbriconereis 

 from running water in Trinidad, 1 a Sabellid, Manayunkia 

 speciosa, 2 from Philadelphia ; and another Sabellid, Coabangiaf 

 from fresh water at Tonquin, which lives in borings in shells 

 of Melania ; and it is by no means improbable that other fresh- 

 water Polychaetes exist in Lake Tanganyika in Africa, where a 

 Medusa has recently been discovered. 



In brackish water of various densities many Polychaetes live ; 

 Arenieola especially is regardless of the character of the medium, 

 and Nereis diversicolor appears to withstand considerable admix- 

 ture of fresh water. 



The majority of the Polychaetes occur " inshore," that is, be- 

 tween tide-marks and in shallow water down to 2 fathoms ; but 

 they occur at all depths more or less abundantly, and some have 

 been dredged from depths of more than 3000 fathoms. 



The nature of the soil composing the shore has a good deal 

 to do with the number of worms to be found there ; thus in cal- 

 careous districts they are fewer than in places where harder rocks, 



1 von Kennel, Arb. Zool. Instit. Wiirzburg, vi. 1883, p. 259. 



2 Leidy, Proc. Acad. Nat. Hist. Philadelphia, 1883, p. 204. 



3 Giard, C. R. Soc. Biol. v. 1893, p. 473. 



