SERPUL^E. 



415 



m ifm 



Terebella Conchilega. 



Serpula G'ontortnplicata. 



Sabella Unispira, 

 Sabella Alveolaria. 



true architects, not inhabiting the tubes which have been con- 

 structed by other creatures, but making them gradually, and in 

 some instances getting together sand, stones, mud, shells, and 

 other objects, which they use as materials for their homes. We 

 may call the caddis grubs, which have recently been described, 

 the tubicolous larva? of fresh water, and very curious are the 

 habitations which they construct. In salt water, however, there 

 is much more variety than in ponds and rivers, and the tubicolge 

 are many and diversified. 



We will begin with those which are most plentiful, and which 

 are best known, because the hardness of their tubes causes them 

 to be preserved long after the inhabitants have perished. If the 

 reader should happen to have used a dredge, or a trawl, he must 

 have brought to the surface great numbers of white shelly tubes, 

 some of them being nearly triangular, and adhering by their 



