TUBE-MAKERS. 329 



which the walls of the tubes are composed, the 

 aperture, usually circular, a little expanded, and often 

 tinged with purple. 



The animal is thus described : The body is less 

 than an inch in length, of a somewhat quadrangular 

 form, slightly tapered from the front to the tail, 

 which is terminated with a narrow caudal appendage, 

 usually curved, or bent upon the back ; the foremost 

 portion is generally coloured with purple, the abdo- 

 minal region is straw colour, becoming pink or fine 

 red at the posterior extremity. The head has the 

 form of a circular disk, divided by a slit into two 

 equal halves, and consists of three concentric rows of 

 bristles, which have a pearly appearance. In the 

 centre of the disk is the mouth, in the form of an 

 elliptical fissure, surrounded with the inner row of 

 bristles bent towards the orifice. The bristles are 

 triangular, tapering upwards to a point, and striated 

 crosswise. The bristles of the middle circle have a 

 bulged, somewhat triangular head, supported on a 

 narrow stalk. The marginal bristles point outwards 

 each resembling a fork, with from five to seven 

 unequal prongs, with the shaft flattened in the upper 

 portion. 



One of the commonest species of British Sabella 

 (Sabella penicillus) has been well described by 

 different authors. " The life of this species is an 

 interesting history. Analogy leads us to believe 



