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When the terebella is withdrawn by force from its tube, it 
