CHAPTEE VI. 



BEISTLE-WORMS continued. 



The Nereids Formation of Heteronerete Characters of Heteronereis 

 The common species and their habits Two sand-worms, Neph- 

 thys and Glycera Their structure and habits The rag- worms 

 The worm Cirratulus The Terebellids and the process of tube- 

 building The tube of Pectinaria Trophonia plumosa The 

 Sabellids and Serpulids The tube-building of Sabellaria The 

 "living film " Ribbon- worms Polyzoa. 



THE family with which this chapter opens is one contain- 

 ing a number of large and common forms. It is the 

 !N"ereida3, to which the genus Nereis, described in the pre- 

 ceding chapter, belongs. As intimated there, by far the 

 commonest species, on Northern coasts at least, is Nereis 

 pelagica, which occurs abundantly between tide -marks, vary- 

 ing in size from two to six or more inches. It is usually of 

 a fine bronze colour, and is an active and handsome form, 

 showing not a little colour variation. 

 As to the species marks, the easiest 

 way of recognising it is to examine 

 the little teeth, or paragnaths, on 

 the introvert see Fig. 35), but it is 

 also characterised by the great size 

 of the palps, the elongated shape 

 of the head, the long dorsal cirri, 

 and the arched back. It may be 

 well to notice that in Nereis the 

 palps are readily distinguished from 

 tentacles by their shape and size. 

 This is not invariably the case, 

 but the two may always be dis- 

 tinguished by the fact that while 



104 



a 6 



FIG. 35. Upper (a) and 

 under (6) surface of the 

 introvert of Nereis pela- 

 gica; j, jaws. The dark 

 specks are the paragnaths, 

 which vary slightly in 

 different specimens. After 

 Ehlers. 



