[385] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 91 
found to have a very long, slender, smooth, soft, whitish body, tapering 
somewhat toward the outer or posterior end, (fig. 1,) which has a muscu- 
lar, circularly wrinkled collar, (¢,) by which the animal is, when living, 
attached to the inside of the shelly lining of its tube. To the inside of 
this collar two shelly plates, known as the “ pallets,” (p,) are attached 
by their slender basal prolongations ; their outer portions are broad and 
flat, and more or less emarginate or two-horned at theend. These are’ 
so connected with the muscles that when the animal withdraws its tubes 
into its hole the free ends of these pallets are made to fold together and 
close the opening, thus serving as an operculum to protect the soft tubes 
against enemies of all kinds. Between the bases of the pallets arise 
the siphonal tubes, (¢,) which are soft and retractile, united together for 
half their length or more, but separate and divergent beyond ; they are 
nearly equal, but the ventral or branchial tube is perhaps a little 
larger than the other, and is fringed with a few small papille at the 
end; the tubes are white or yellowish, sometimes specked with reddish- 
brown. At the anterior end of the body and farthest from the external 
opening of the hole, is seen the small, but elegantly sculptured, white 
bivalve shell, (cut 2,s; and Plate X XVI, fig. 183, s.) The shell covers the 
mouth and palpi, liver, foot, and other important organs. The foot (/) 
is a short, stout, muscular organ, broadly truncate or rounded at the end, 
- and appears to be the organ by means of which the excavation of the bur- 
row is effected. The shell is covered by a delicate epidermis, and prob- 
ably does not assist in rasping off the wood, as many have supposed. 
The gills are long and narrow, inclosed mostly in the naked part of the 
body, and are reddish brown in color. The Teredos obtain their micro- 
scopic food in the same manner as other bivalve mollusks, viz., by 
means of a current of water constantly drawn into the branchial tube by 
the action of vibrating cilia within; the infusoria and other minute or- 
ganisms are thus carried along to the mouth at the other end, while the 
gills are supplied with oxygen by the same current; the return current 
passing out of the dorsal tube removes the waste water from. the 
gills, together with the feeces and excretions of the animal, and also the 
particles of wood which have been removed by the excavating process. 
As the animal grows larger the burrows are deepened, the lining of 
shelly matter increases in length and thickness, the shell itself and the 
pallets increase in size, and the terminal tubes grow longer. But as the 
-orifices of the terminal tubes must necessarily be kept at the external 
opening of the burrow, the muscular collar at the base of the tubes con- 
stantly recedes from the entrance, and with it the pallets; at the same 
time imbricated layers of shelly matter are usually deposited in the 
upper end of the shelly tube, which are supposed to aid the pallets in 
closing the aperture when the tubes are withdrawn. When the animal 
has completed its growth, or when it has encountered the tubes of its 
companions and cannot pass them, or when it approaches the exterior 
of a thin piece of wood and cannot turn aside,it forms a rounded or 
8V 
