32 



TEREDO. 



from the rocky home where they have Hved and 

 died. In the interior of a perfect shell may be 

 seen a very curious projection, formed something \ 

 like a spoon. Its object does not seem to be very 

 clearly ascertained. The tube, which has been 

 so often mentioned, is generally a composite 

 organ, composed of two tubes or siphons, as they 

 are called, which are placed closely together, 

 something on the principle of a double-barrelled 

 gun, or an elephant's trunk. Through these 

 tubes passes the water which is necessary for 

 respiration, being received into one tube, drawn 

 from thence over the gills, and finally expelled 

 from the other tube. 



There is another boring mollusc, which is on 

 many accounts worthy of notice. This is the so- 

 called Shipworm (Teredo navalis), a representa- 

 tion of which may be found on plate F, fig. 3. 

 It has been placed on the same page with some 

 of the worms, in order to show its very great 

 external resemblance to some animals of that 

 class, and especially its similitude to the Serpula. 

 So closely, indeed, does it resemble the last 

 named creature, that even Linnaeus placed the 

 Teredo between Serpula and Sabella in his 

 " System of Nature." 



But this is really one of the molluscs, and a 



