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 

 always 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. 



