138 TEREDINID^E. 



Saxicava, Gastrochana, andPholas, but also the common 

 oyster. I now take leave of this curious subject, be- 

 lieving that it has been sufficiently discussed or venti- 

 lated (" soaked " is the term which an English statesman 

 lately invented) ; and all naturalists, who take an inter- 

 est in it, may adopt whichever theory they prefer, be 

 it chemical, conchological, or malacological in other 

 words, that the excavation is caused by the solvent 

 power of an acid, the rasping action of the shell, or the 

 sucker-like application of the foot. This is a very long 

 commentary, and I am afraid it will terribly " bore v many 

 of my readers; so I will resume the analysis of Sellius's 

 monograph. The quantity of water taken in and re- 

 tained by the Teredo is prodigious : Sellius not inaptly 

 compared the animal to an hydraulic machine. I feel 

 the same admiration that he avowed of the wonderful 

 sagacity shown by the Teredo in making its way through 

 a piece of wood, so as to avoid the tubes of other indi- 

 viduals. Every one pursues its own course with unerring 

 instinct ; and it must be gifted with some organ of sense 

 or apprehension, more delicate than we can conceive, 

 in order that it may be aware when it approaches an- 

 other Teredo. The sheaths are never contiguous, but 

 in every instance separated by an intervening layer of 

 wood. The Teredo uses its pallets as a means of defence 

 against its enemies, by closing the opening of the canal, 

 thus 



" . . . . omnem aditum custode coronans." 



He rightly described them as inserted in a sphincter- 

 like ligament at the base of the siphons. The function 

 of these processes is identical with that of the operculum 

 in many univalves although they are not homologous, 

 or produced by similar organs. He next considered the 

 sexuality of the Teredo. His assertion that it is her- 



