CONSTRUCTION OF SANDY TUBE. 279 



It is very interesting to watch the modus operandi of 

 these quiet labourers ; and the curious observer,, who 

 desires a distinct view of their operations, ought so 

 to contrive matters that their advancing tube should 

 come in contact with the sides of the aquarium. They 

 then continue alike industrious ; but frequently, as if 

 to economise labour, the growing edifice is reduced 

 to the segment of a cylinder, the transparent glass 

 supplying the defective portion : in this manner, what- 

 ever passes within is sufficiently exposed. A Sabella, 

 previously carrying on its operations in a watch-glass, 

 will sometimes avail itself of the transparent side of 

 a jar in the same manner. The greatest activity is 

 alw r ays displayed during the warmest weather. 



These animals quit their tubes when the water 

 becomes vitiated, and sometimes without any such 

 reason; seeming to suffer little inconvenience from 

 the want of them. 



Their food is unknown; nevertheless, they are 

 easily preserved, specimens having been found to live 

 thirteen months in confinement. 



