SOLENOCONCHIA. 187 



to the funnel- shaped mouth, in which, by the aid of 

 labial and ciliated palps, the animalcula are quickly en- 

 gulfed : 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 central tooth is usually called 

 a " rachis," and the side teeth " pleurse ; " they are ar- 

 ranged thus, 2.1.2. The front set of pleurse are armed 

 with crochets or " uncini." The apparatus now described 

 seems to have an office analogous to that of the tongue 

 in many cephalophorous mollusks, and it is certainly not 

 a gizzard as Mr. Clark supposed. The shelled Forami- 

 nifera found in the stomach of a Dentalium are perfect, 

 and the sarcode must be extracted from them by some 

 secretion answering to the gastric juice of the Verte- 

 brata. Dentalium has no eyes ; they would be useless 

 to an animal always buried in 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 tremulous movement. The 

 organs of circulation and respiration are of a rudimen- 

 tary kind ; there is no heart. The sexes are separate. 

 There are no external organs of generation; but im- 

 pregnation is effected by the male emitting his sperma- 

 tozoa, and the female her eggs at the same time, in the 

 water. The process may be partly 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 fecundation. 

 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 decom- 



