ANAETHEOPODA. 



133 



FiL'. 84. — Tuliicola. rt Serinila contor- 

 iHpUcalu, sliowiii,' tlif- lintncliiiH and 



veniently divided into two groups, according as they secrete for 

 themselves a protective tube {Tuhicola), or live a free life (Er- 

 rantid) ; but the general organisation in these two sections is essen- 

 tially the same. 



The Tubicolous Annelides or Tube-worms derive their name from 

 the fact that they have the power of protecting themselves by 

 means of tubes (Lat. tuba, a tube ; 

 and colo, I inhabit). In some cases 

 (fig. 84) the tube is composed of 

 carbonate of lime, ;ind is a genuine 

 secretion from the body. In other 

 cases, the tube is composed of 

 grains of sand or pieces of broken 

 shell, cemented together by a glut- 

 inous secretion from the surface of 

 the body. In all the Tuhicola the 

 respiratory organs are in the form 

 of branched filamentous external 

 gills, in which the fluid of tlie 

 pseudohtemal system is suljjected 

 to the action of the outer watei'. 

 They are therefore " Branchiate " 

 Annelides. As they live in tubes, 



however, and do not voluntarily expose m(jre than the anterior end 

 of the body, the branchite are all ])laced on or near the head. Tlie 

 filaments of which the gills ar.e composed (fig. 84, n) are richly 

 ciliatetl, and as the pseudohtemal fluid is usually red, tliey have 

 generally a beautiful scarlet coloui'. 



The most familiar of the Tuhirola is the Herpida (fig. 84, «), the 

 contorted and winding tubes of which must be knowir to every 

 one as occurring on shells or stones on the sea-shore. One of the 

 cephalic filaments in Hvrpula is much develojjed, and its extrem- 

 ity forms a kind of conical plug or "operculum," which serves to 

 close the mouth of the tube when the animal is reti'aeted within 

 it. In Spirorhis (fig. 84, h) the shelly tube is coiled into a flat 

 spiral, which is fixed to some solid object. It is of extremely com- 

 mon occurrence on the fronds of sea-weed, and on other submarine 

 obj :^cts. 



The so-called "Errant" Annelides (Lat. erro, I wander) are so 

 called because of their " roving " habits, the animal leading a free 

 existence, and not being confined in a tube (fig. 85). They have 

 always lateral unjointed appendages, or foot-tubercles, which carry 

 tufts of bristles, and a soft jointed filament or cirrus. The anterior 

 rings of the body are usuiiUy so modified as to foi-m a sort of head, 

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