i6o 



THE BOOK OF NATURE STUDY 



and the attempt to pull up one of those in the natural position 

 in the sand will also merely produce a fragment of empty tube. 

 The reason is that the worms reach a considerable length, 10 

 inches or so, and their tubes are always much longer than them- 

 selves, so that when a tube is pulled up the worm retreats to the 

 bottom, and it is only a few inches of tube that is obtained in this 

 way. A spade will enable you to obtain perfect specimens of 

 tubes and worms, but success in the aquarium is more likely to 

 be obtained with some of the smaller species found under stones 

 than with the sand-mason proper, the most conspicuous form. 

 The structure of all the common Terebellids is approximately 

 similar, and the points to observe are, first, the tube, which is 

 made by the long red tentacles which the uninjured worm can 

 protrude from the mouth of its tube. When the worm does this 

 in the aquarium it is possible to see how the delicate red tentacles 

 are sheltered within the sandy fringe of the 

 tube, and when the tentacles are fully pro- 

 truded one can make out that mingled with 

 them are the delicately branched gills, by means 

 of which the worm breathes. On an alarm it 

 can shoot back again into its tube with great 

 rapidity, by means of a wonderful series of 

 hooks with which the body is furnished for the 

 purpose. All these points are shown in Fig. 79. 

 Another worm which makes a tube of par- 

 ticles of sand is the comb-worm (Pectinaria 

 belgica), so called because of the beautiful 

 comb of golden bristles with which the head 

 is furnished. The tube in this case is short, 

 about ij inch in length only, but is most 

 beautifully made, and the animal shows some 

 analogy to a caddis-worm (q.v.} in that it carries 

 its tube about with it, and does not remain 

 permanently in one spot like the Terebellids. 



Another type of tube is that found in the 

 Serpulid worms. Here the tube is made of lime, 

 and is often coiled. When the worm is alarmed it retreats com- 

 pletely into its hard tube and closes the opening with a curious 



P 



tp 



FIG. 80. The comb- 

 worm (Pectinaria 

 belgica} removed 

 from its tube, c, 

 " comb " of bristles ; 

 /, tentacles ; g y gills ; 

 p, parapodia ; tp, ter- 

 minal plate which 

 closes posterior end 

 of tube. 



