ON ANNELIDA. . 85 



terior pair is much smaller than the others, and especially 

 than the two middle ones. Their termination takes place ex- 

 ternally, by very small orifices situated between the fifth and 

 sixth pair of feet, for the fourth pair ; between the fourth and 

 fifth for the third ; between the fourth and second for the 

 second ; and between the third and last, for the first. 



These animals live often assembled in great numbers, in 

 those parts of our coasts where plenty of sand is to be found ; 

 and especially argillaceous sand, for, although their tube 

 often contains sand, properly so called, fragments of shells 

 enter still more into its composition. These tubes often ex- 

 ceed, by two or three inches, the surface of the ground in 

 which they are implanted. When the sea covers them, we 

 see the animal put forth its barbies and gills, and agitate them 

 in all directions. The last are of a fine blood-red, and have 

 so much sensibility, that if they are touched, they contract, 

 the blood is expelled from them, and they are no longer red. 

 The barbies of the mouth are not coloured by the blood. 

 They are in a perpetual movement of contortion, of extension, 

 and through a property dependent, no doubt, on the mucous 

 matter secreted by their surface, as well as on the particular 

 foiTQ of their inferior face, they adhere with a great facility to 

 all the bodies which they touch. It is, in fact, with the as- 

 sistance of these organs, that the terebella constructs its tube ; 

 its base is a glutinous membrane, to the surface of which the 

 foreign bodies are cemented. They are pretty nearly cylin- 

 drical, a little narrowed, however, behind, but broadly opened 

 upon that side, as well as the other. They are uncovered for 

 the space of an inch from their origin. Some appear to have 

 been found totally so, as Pallas notices in the case of indi- 

 viduals, which he has observed on the masses of eggs of the 

 buccinum undulatum. 



When the terebella is withdrawn by force from its tube, it 



