112 DENTALIID^. 



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 

 6rgans. 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 animalcules 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 s]3herical 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 dioecious 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 

 eggs 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 larvse 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 

 diiring 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 fty die, Paramecia and Ploesconise (infu- 

 soria) are bred from the decaying matter, and, entering the shells 



