34 6 



TOILERS IN THE SEA. 



FIG. 68 (Pholas dactylus}. 



\ tself at last to a very simple 

 process, of continuous motion 

 in a given direction, without 

 any assistance from a sup- 

 posed acid secretion, which 

 earlier authors considered ne- 

 cessary to dissolve the rock 

 operated upon (fig. 68). 



There is also another ex- 

 cavating mollusk (Xylophaga 

 dorsalis] which causes con- 

 siderable damage to timber 

 work about docks, and to 

 that of piers and jetties. It 

 attacks timber of all kinds 

 that are under water in the 

 neighbourhood of quays. 

 " Like the Teredo, it inhabits 

 the interior of wood, which 

 has been some time under 

 salt water, penetrating to the 

 depth of from half an inch to 

 an inch, forming for itself an 

 oval receptacle or cavity, and 

 having a very small and single 

 external orifice." 1 It differs 



1 Mr. W. Thompson " On Xylophaga Dorsalis? &c., in 

 "Annals of Nat. Hist.," vol. xx. (1847), p. 157. 



