84 SEA-SIDE STUDIES. 



Very different, and far more philosopliical, is the explana- 

 tion of Professor Owen, whose opinion on all points carries 

 authority. He shows* that the combined action of the 

 muscular disc and the valves of the shell will produce the 

 phenomenon. It may be paradoxical, and you will probably 

 shake a dubious head on seeing the cavities bored by these 

 Molluscs, and on being told that the soft muscular disc of 

 the animal perforated them ; you have no conception that, 

 by licking limestone with never so much energy, you could 

 wear it away ; and yet, as Owen quietly remarks, " it is 

 certain that the perpetual renewal of a softer substance will 

 render it capable of wearing away a harder one, subject to 

 the friction of such softer surface, and not like it susceptible 

 of being repaired." Yes, here lies the whole mystery : the 

 soft muscular disc is perpetually renewed, and the hard 

 limestone has no self-renovating power ; and thus, just as 

 falling water wears away granite, by the incessant repetition 

 of gentle blows, so do these Molluscs excavate rock, or wood, 

 by the incessant repetition of muscular friction, -f- 



Some practical man, wdio does me the honour to relax 

 his serious mind over these pages, here declares himself 

 supremely indifferent to this anatomical discussion. What 

 does it signify to him how the Teredo bores into the wood ? 

 He is none the better for that. It is enough for him 

 that the nasty beast does it, and unless he can be told 

 how it is to be prevented, he wants to hear nothing about 



• Lectures on Cumimralive Anatomy, i. 520. 



t Victor Carus — Juhrcs1,erich( ilhenlie im Gehieie d. Zootomie erschienenen 

 Arhdtcn, i. 110 — gives a dozen references to papers on this question. 



