112 DENTALIIDA. 
minute organisms, which it catches with its thread-like tentacles. 
These are all lengths and sizes, and are insinuated among the 
grains of sand on every side; they are covered with ‘cilia, 
especially at the points, which resemble suckers. They are 
thrown off by the Dentalium under certain conditions, and may 
occasionally be seen detached and wriggling like taper hair- 
worms. Terebella and other tubular annelids have similar 
organs. Being highly contractile, these tentacles convey the 
food to the funnel-shaped mouth, in which, by the aid of the 
labial and ciliated palps, the animaleule are quickly engulfed ; 
then the masticatory apparatus comes into play. This consists 
of a tongue or lingual riband, armed with five rows of sharp 
spines, one in the middle, and two on each side. 
“The shelled Foraminifera found in the stomach of a Denta- 
lium are perfect, and the sarcode must be extracted from them 
by some secretion answering to the gastric juice of the Verte- 
brata. The Dentalium has no eyes; they would be useless to an 
animal always buried in the sand. They have otolites or ear- 
stones, which serve as organs of hearing; these are extremely 
numerous, calcareous and globular, and are enclosed in two 
nearly spherical pouches, lined with vibratile cilia, which are in 
constant action, and agitate the otolites by an incessant tremu- 
lous movement. The organs of circulation and respiration are 
of a rudimentary kind; there is no heart. The sexes are 
separate. There are no external organs of generation, but 
impregnation is effected by the male emitting his spermatozoa, 
and the female her eggs at the same time in the water. The 
process may be compared to the chance shedding of pollen in 
the air by dicecious plants. Lacaze-Duthiers noticed that the 
spermatozoa lived six hours after performing the act of fecund- 
ation. The egg is at first oval, afterwards pear-shaped, and 
ultimately divided into segments like those of an Annelid. Such 
egos as do not arrive at maturity speedily decompose and are 
cleared out by swarms of infusoria, which appear to be generated 
from the corruption. In the first stage of development the germ 
is motionless; in the second stage it is propelled by vibratile 
cilia, which are set around a large lobe in front, similar to that 
observable in the larvee of many mollusca, and it swims rapidly; 
in the third stage it crawls by means of a disk-like foot. In 
swimming it does not come to the surface of the water, as do 
the fry of the oyster and other mollusca. The shell is formed 
during the third period, but is only detected by its iridescent 
lustre, being exceedingly thin and transparent, a mere film. This 
state continues until the fifth and occasionally the sixth day 
after birth. The embryonic period lasts from thirty-five to forty 
days. If any of the fry die, Paramecia and Ploesconiz (infu- 
soria) are bred from the decaying matter, and, entering the shells 
