186 



THE SEA SHORE 



If a cluster of these tubes, freshly gathered from between the 

 tide-marks, be placed in the aquarium, the worms will soon 

 protrude the foremost portion of their bodies, exposing beautiful 

 fan-like gills, often brilliantly coloured in shades of scarlet, blue, or 

 purple, which are kept in motion in such a manner as to convey 

 water, and consequently also food, towards the mouth. The gills 

 are of course, richly supplied with blood, for their main function is 

 to aerate that liquid by exposing it to the water in order to absorb 



oxygen gas. The body of the 

 worm is provided also with 

 little cilia, which, by their 

 constant vibratory motion, 

 keep up a circulation of water 

 through the tube ; and this 

 not only keeps the tubular 

 home free from excrement 

 and other sedimentary mat- 

 ter, but also probably assists 

 in the function of respiration 

 by bringing fresh supplies of 

 water in contact with the 

 animal's soft and absorbent 

 skin. 



When the worms are 

 disturbed they immediately 

 withdraw themselves within 

 the tubes, this being done 

 by the aid of the numerous 

 minute booklets on the sur- 

 face of the body that enable 

 the worms to cling firmly to 

 the membranous linings of 



their homes ; and it will then be observed that the mouth of each 

 tube is closed by a lid (operculum), which hangs as by a hinge when 

 not in use. These operculi vary much in character, and supply 

 another aid in the identification of the various species. They 

 differ much in shape, and may be either membranous, horny, or 

 calcareous. 



Little calcareous tubes, somewhat similar to those of the Serpulce, 

 but always in the form of a spiral, may often be seen on stones and 

 shells, and the fronds of sea weeds, sometimes so closely packed 



FIG. 122. Serpula REMOVED TBOM 

 ITS TUBE 



