and Teredo Navalis , 
28 9 
the teredo navalis, like the teredo gigantea, forms its habita- 
tion in a substance from which it receives no part of its suste- 
nance : and that the sawdust conveyed through the intestines is 
not digested, particularly as that examined by Mr. Hatchett* 
had not undergone the slightest change. 
The straight course of the intestine in the teredines makes it 
probable that the sawdust retards the progress of the food, 
so as to render convolutions unnecessary. In some of the 
actineae from the West Indies, the intestine is so much convo- 
luted, that it appears to be wound round a central cylinder, in 
closely compacted turns. 
EXPLANATION OF THE PLATES. 
Plate XII. 
Fig. 1, Represents a portion of the teredo navalis in its 
shell inclosed in the wood, to show the manner in which the 
two tubes are protruded, and the appearance of the shell at 
its termination, which is contracted but not divided into two 
canals as in that of the teredo gigantea. 
Fig. 2, Represents the teredo belonging to the British 
Museum, the opercula are wanting, and the tubes are re- 
tracted. 
aa, Are the boring shells. 
b, The proboscis. 
c, The mouth. 
dd , The contents of the abdomen seen through the trans- 
parent external covering. 
ee, The breathing organs seen in the same way. 
P p 2 
