138 TEREDINIDzE. 



Saxicava, GastrochcBna, andPholas, but also the common 

 oyster. I now take leave of this cui'ious 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^^ 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 hydi'aulic 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 OAvn 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 Tei^edo uses its pallets as a means of defence 

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

 thus 



" . . . . oiunem 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 

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



