280 Mr. Home on the Teredo Gigantea 
shell. The body of the animal fills the area of the shell com- 
pletely : but appears much smaller when taken out, in conse- 
quence of the sea water, which it contained, having escaped. 
The worms that were examined were of very different 
lengths. The largest is represented in the annexed drawing, 
(Plate XII. Fig. 1,) and was 8 inches long. Many of them 
were alive 24 hours after being removed from their shell : 
and in these the heart was distinctly seen to palpitate. The 
blood contained in the vessels going to the head was of a red 
colour, as also the parts near the liver ; but this colour disap- 
peared soon after death. 
The head of the worm is inclosed between the two boring 
shells, which are concave, so that the face, if the expression 
is admissible, is the only part exposed. The shells in their 
external form are sufficiently displayed in the drawings, to 
make a particular description of them unnecessary. 
The shells are united together, on what may be called the 
back part of the head by a very strong digastric muscle, hav- 
ing a middle tendon, from which the fibres go off in a some- 
what radiated direction, partly to be inserted into the concave 
surface of each shell, and partly into a long semicircular 
process, projecting from the posterior part of each shell. The 
two inclose the oesaphagus, and other parts surrounding it. 
The form of the process is shewn in the annexed drawing. 
The double muscle is inclosed in a smooth shining fascia. 
When first exposed it was of a bright red colour. 
On the opposite side of the head the shells are united by a 
ligament, from which they are readily separated ; at this part 
there are two small tooth-like processes ; one from the 
narrow edge of each shell, where they are joined together. 
