8 Observations upon the Habits, Structure and (January, 
brief periods, did it ever disappear beneath the surface. Gener- 
ally it lay flat upon the top of the sand, until disturbed from its 
repose, when its actions closely resembled those of its smaller 
fellows. Hence it must be at a later period of life than that to 
which this one had attained, that these little animals cease to be 
shifted about by the flood and ebb of changing currents, and 
become “burrowers.’ The adults, which were taken from the 
banks by means of the dredge, were placed together in a large 
jar of sea-water, which was furnished, like the dish of the largest 
of the young animals, with a layer of sand upon the bottom. 
When once in the water they commenced swimming about very 
rapidly, with the same graceful, undulating motion which has 
been noticed as characteristic of the young, but with much 
greater vigor and elasticity. These movements were executed 
sometimes upon the back, sometimes upon the abdomen in the 
position of ordinary fishes, it seemed to make very little differ- 
ence which side was uppermost, but I have never seen them 
move backwards, or tail-end foremost. After circumnavigating the — 
vessel once or twice, gradually moving slower and slower, they 
would stop and sink down upon the sand at the bottom. Gener- 
ally as soon as they touched the sand they would half-arch their 
bodies and almost instantaneously disappear from sight beneath 
the surface, thus regaining their natural place of refuge. After 
this disappearance they very rarely entirely emerged from their 
retreat, and as a rule, not at all during the day time. But if the 
surface of the sand was carefully examined at night, little spots 
might be detected where the sand appeared less compact than 
elsewhere, and a close inspection would discover each such spot 
to be a network of crossing tentacles arching over the expanded 
mouth cavity of one of these animals, which was thus, while 
lying belly upwards buried in the sand with only its mouth 
exposed at the surface, busily engaged in drawing its food from 
the water above. 
Sometimes they could be found so situated during the day 
time, and now and then both by day and night, but rarely in the 
day time, one or more of them could be seen protruding part 
way from the sand, and looking as if planted in this position, but 
a tap or a motion of the vessel would cause them to withdraw, ‘ 
from sight immediately. 
These actions would seem to indiai what is B a fact, ` 
