PRACTICAL CONSEQUENCES OF THEORY. 89 



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* 



Some practical man, who does me the honour to re- 

 lax his serious mind over these pages, here declares 

 himself supremely indifferent to this anatomical dis- 

 cussion. What does it signify to him hoiv 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 the matter. As a prac- 

 tical man, he wants practical applications ; as for 

 " theories,'' he doesn't care a silver fourpence for them. 

 I will not turn round and humiliate him, by proving 

 that of all blind theorists none are blinder than the 

 "practical men;" but will rather captivate his confi- 

 dence, by showing him how the result he so earnestly 

 desires is only to be obtained after a remote excursion 

 into the obscure regions of science. He need not make 

 the excm^sion, but he must wait till it be made ; for it 

 is amusing to think that even so simple a matter as 

 the destruction of these vermin defied all ingenuity, 

 until Embryology came to our aid. I carefully abstain 

 from mentioning that unusual term in his presence, 

 but address a question to him : — 



" Are these animals of separate sexes ?" 



* Victor Carus — Jahresbericht ilher die im Gehiete d. Zootomie ersch- 

 ienenen Arbeiten, i. 110 — gives a dozen references to papers on this 

 question. 



