SEEPULffi. 397 



has a very slight curve, is sharply pointed, and is armed with a 

 double row of barbs on the edge. A great number of these 

 bristles are clustered together, so that their united force is really 

 considerable. 



Supposing that the animal is fully expanded, and that the 

 observer has succeeded in placing his eye to the glass without 

 alarming the sensitive creature, he will see a wonderful sight. 

 In its way there is nothing which surpasses in beauty the ex- 

 panded gill-tuft of a Serpula in perfect health. The long feathery 

 gills radiate from the tube in a curve which combines grace and 

 force in no ordinary degree, while the beautiful colours that glow 

 as the blood courses through their translucent substances are far 

 beyond the power of description. 



One use of the gills is evident enough. They serve for respira- 

 tion. But they also answer another purpose, and aid the animal 

 in procuring food. Being necessarily stationary, it cannot roam 

 about in search of food, and its appetite is so great, that it would 

 soon die were it to depend for subsistence on the nourishment 

 which might be brought within its reach by the waves. 



If a tolembly powerful glass can be brought within the neces- 

 sary focal distance, it will be seen that the exterior of the gill- 

 tufts is covered with wonderfully delicate filaments, or cilia, as 

 they are technically named, which are continually waving in 

 regular ripples. Their movement constitutes a sharp current of 

 water, which not only washes against the gills and furnishes the 

 requisite supply of air for the regeneration of the blood, but 

 carries the water downwards into the mouth, which opens at the 

 bottom of the gQl-tufts. In the water is always a bountiful 

 supply of minute animal organisms, together with other sub- 

 stances, which, although microscopically small, are in the aggregate 

 sufficient to feed the Serpula. This current is kept continually 

 flowing as long as the tentacles are protruded, and thus the 

 creature is enabled to breathe, is supplied with nourishment, 

 and the tube is kept clean by the water current which is per- 

 petually rushing through it. 



We now come to that wonderful portion of the animal which 

 is called by naturalists the " operculum," and which is popularly 

 and rightly known as the " stopper." This is the conical appen- 

 dage which hangs from the tube, and is used in closing its mouth 

 when the gills have been withdrawn. The operculum is known 



