168 LECTURE XL 



considered rather as forming a general outline 

 than a minute and strictly accurate illustration of 

 the subject. 



Among those genera whose inhabiting animal 

 differs from the rest as to its nature, the genus 

 De.ntalium is an example : the shell is shaped 

 like an Elephant's tusk in miniature, and its 

 inhabiting animal is supposed to be allied to a 

 Terebella. The genus Serpula is of various shape 

 in the different species, but is generally of an ir- 

 regularly twisted appearance, resembling a long 

 tube warped in different directions. Its inhabit- 

 ant is also supposed to resemble a Terebella. 



The genus Teredo is in reality a kind of naked 

 worm, which lines with a shelly matter the wind- 

 ing or irregular cavities w r hich it forms in wood or 

 other substances : its head is armed with a pair of 

 very strong calcarious or shelly jaws, with which 

 it works its way into the substance it inhabits, 

 which is generally the wood of the bottoms of 

 ships. This is the celebrated and destructive 

 animal called the Ship-Worm, the Teredo naralis 

 of Linnaeus,, so formidable for its ravages, and 

 which hardly any contrivances yet suggested by 

 human ingenuity have been found fully sufficient 

 to prevent. Thus a contemptible worm, multiply- 



