96 MARINE ANIMALS OF MASSACHUSETTS BAY. 



smaller particles with their tentacles, and making a ring around 

 their anterior extremity. This ring they then push down along 

 the length of the body, and continue this process, adding ring 

 after ring, till they have entirely encircled themselves with a 

 sand tube. They move the rings clown partly by means of con- 

 tractions of the body, but also by the aid of innumerable append- 

 ages over the whole surface. To the naked eye these appendages 

 appear like little specks on the skin ; but under the microscope 

 they are seen to be warts projecting from the surface, each one 

 containing a little anchor with the arms turned upward (Fig. 

 125). Around the mouth these warts are larger, but do not 



contain any anchors. It will be seen here- 

 after that these appendages are homologous 

 with certain organs in other Holothurians, 

 the warts with the anchors correspond- 

 ing to the limestone pavement covering 

 or partially covering the surface of the 

 Cuvieria, for instance, while those without 

 anchors correspond to the so-called false 

 ambulacra in Pentacta. By means of these 

 appendages, though aided also by the con- 

 tractions of the body, the Synaptas move 

 through the mud and collect around them- 

 selves the sand tube in which they are en- 

 cased. Their food is very coarse for animals so delicate in struc- 

 ture. When completely empty of food they are white, perfectly 

 transparent, and the spiral tube forming the digestive cavity may 

 be seen wound up and hanging loosely in the centre for the whole 

 length of the body. In such a condition it is of a pale yellow 

 color. But look at one that is gorged with food. The whole 

 length of the alimentary canal is then crowded with sand, peb- 

 bles, and shells, distinctly seen through the transparent skin, and 

 giving a dark gray color to the whole body. They swallow the 

 sand for the sake of the nutritious substance it contains, and 

 having assimilated and digested this, they then eject the harder 

 materials. The motion of the body in consequence of its contrac- 



Fig. 125. Anchor of Synapta ; a anchor, w plate upon which anchor is attached ; greatly mag- 

 nified. 



