INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 385 



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, (c,) 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 the end. 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 papillae at the 

 end 5 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 XXVI, 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 j 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 fseces and excretions of the animal, and also the 

 particles of wood which have been removed by the excavating i^rocess. 

 As the animal grows larger the burrows are deepened, the lining of 

 shelly matter increases in length and thickness, the shell itself and the 

 l)allets 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 

 S. Mis. 61 25 



