ZOOLOGICAL SOCIETY BULLETIN 
141 
their breeding season and the conditions under 
which they live. 
Very few persons are acquainted with the 
appearance of real shipworms because these 
animals live in wood most of their lives. To 
study them one must carefully carve open 
their burrows with chisels, and extract them 
without injuring their delicate translucent 
bodies. Shipworms are not worms at all but are 
inollusca, related to clams. They are highly 
specialized for boring into wood and thus out¬ 
wardly resemble a clam very little although in 
their essential structure they are quite similar. 
The shipworms burrow into wood for protection. 
Their homes are lined with a pearly layer 
secreted by the mantle which also produces the 
boring apparatus consisting of two small shells 
corresponding to the shells of a clam or oyster 
but in this case enclosing very little of the soft 
body of the animal. A clam can close up in 
its shell, a teredo can not. He merely uses it 
to drill, depending on the wood in which he 
lives for an impregnable covering. 
These shells are pivoted on knobs above and 
below and rock back and forth. On their outer 
surfaces they have rows of minute teeth which 
chip off the wood. The rocking motion is pro¬ 
duced by two muscles, a smaller one in front 
called the anterior adductor muscle and a larger 
one behind called the posterior adductor muscle. 
The contraction of the latter causes the shells 
to gape more in front and this motion chips 
off the wood at the blind end of the burrow. 
The wooden chips are swallowed to get them 
out of the way and generally pass clear through 
the digestive tract of the teredo. Perhaps 
some sugar-like nutriment is got from the wood 
but that is still unsettled. At anv rate wood 
is not the principal food of the shipworm which 
exists and grows on microscopical plants and 
animals of the sea water. The shell is added 
to as the animal grows by the secretion of a 
fold of the mantle at its posterior border. 
In a clam there is a plow-shaped foot for 
burrowing into the mud or sand. Teredo also 
has a foot but it is modified into an adhesive 
disc and is located at the blind end of the bur¬ 
row between the shells and serves to hold these 
shells tightly to the wood during the boring 
process. Above the foot is a small mouth for 
the reception of food and wood chips. 
Most of the soft body of the shipworm which 
may be a foot long in teredo and three feet 
long in bankia, the feather-tailed shipworm, is 
covered with a delicate mantle. Inside this 
mantle are the vital organs of the animal. 
There are organs of digestion, gills for respira¬ 
tion, organs of circulation, a nervous system 
and reproductive organs. The mantle secretes 
three different parts, the boring shells, the 
lining of the burrow, and a pair of pallets 
which will be described later on. 
The only communication the burrow has with 
the outside world, the sea water, is through a 
little hole not over a sixteenth of an inch in 
diameter. When the shipworm is not disturbed 
there are two tubes thrust out of this hole into 
the water. These are called siphons, incurrent 
and excurrent. Into the former water flows 
whereas from the latter it is discharged. These 
siphons communicate with the mantle cavity 
and the currents of water are produced by its 
cells which have hair-like lashes that, beat 
toward the mouth or in the reverse direction. 
The water flowing into the mantle cavity brings 
food and oxygen to the animal whereas the ex¬ 
current water carries off all the waste materials 
including the wood chips. 
At the base of the siphons on each side of 
the teredo is a pallet. This is a shovel-shaped 
body made up of lime. The blade of the shovel 
is directed toward the small opening at the 
surface of the wood. When the shipworm is 
disturbed the siphons are pulled into the burrow 
and the pallets are thrust into the opening to 
the exterior to keep out the intruder. In teredo 
these pallets are simple structures but in bankia 
they are made up of many pieces and resemble 
feathers. From these pallets bankia gets its 
common name, the feather-tailed shipworm. 
To understand how teredo gets into new 
wood and increases in numbers we must con¬ 
sider how its reproduces. Minute eggs are pro¬ 
duced by millions after the animal is only 
a few months old. Sperm cells escaping through 
the excurrent siphon by the billions are set 
free into the sea water by male individuals. 
The gills of teredo act as breed pouches and 
in these the eggs are shed and here come in 
contact with a constant flow of water. This 
incurrent water contains many teredo sperm 
cells and fertilization takes place. The ferti¬ 
lized eggs develop into little free swimming 
larvae which move by means of a circlet of 
ciliated cells. These pass from the gill pouches 
into the sea with the excurrent water and de¬ 
velop into minute clam-like organisms with two 
little shells, a long movable foot and a sticky 
thread for holding on. In bankia there are 
no breed pouches and eggs and sperm are set 
free into the sea where the entire development 
of the larva takes place. 
