352 TOILERS IN THE SEA. 



struct buried tubes. In structure they correspond 

 in all respects with their congeners of tube-making 

 propensities, and hence will require no special de- 

 scription. Doubtless, they are not by any means 

 guiltless of perforating old shells, and living ones too 

 for that matter, although it is by no means proven 

 that the chambered oyster-shells, lined with sponge, 

 have been at first perforated, as some assert, by small 

 annelids, and afterwards occupied by the sponge. It 

 is difficult to conceive how all the dendritic cavities 

 in shells were excavated by worms, whilst, it must be 

 confessed, that certain forms of excavation bear strong 

 evidence in themselves of their annelid excavators. 

 Direct proofs of such operations are difficult to obtain, 

 inasmuch as they are performed far beyond the reach 

 of prying eyes, and hence much must depend on 

 inference from analogy. Whether there is any real 

 analogy between the operations of a boring annelid, 

 or a boring sponge, and the larvse of a wood-boring 

 beetle (Scolytus}> we will not pronounce, although at 

 least one writer seems to infer that what is true of 

 one must be true of the other. There is at least 

 sufficient resemblance, in the results, to make the 

 gradation easy from the worm to the sponge, and 

 enable us to give here, in fuller detail, what has been 

 affirmed of the latter, which, as Agassiz says, are 

 " perhaps still more destructive " than the former. 

 The boring sponges (Cliona\ are a group of exca- 



