i;8 ECHINODERMATA. PART in. 



of pinnate tubular tentacles. The outer margin of the 

 lip is fringed with a circle of snake-headed pedicellarise 

 visible to the naked eye. 



The five teeth, whose sharp tips meet in a point when 

 closed, are triangular prisms, the inner edge is sharp 

 and fit for cutting. Each tooth is planted upon a 

 larger triangular socket, two sides of which are trans- 

 versely grooved like a file, and as these two sides are in 

 close contact with the sides of the opposite socket, the 

 food when cut by the small teeth is ground down by the 

 sockets, and a salivary secretion finishes the masti- 

 cation. The sockets of the teeth are connected by 

 ten additional solid pieces, placed two and two between 

 them, which completes the pyramidal apparatus called 

 Aristotle's lantern ; it consists of forty solid calcareous 

 pieces arranged in fives, and moved by forty muscles at- 

 tached to five calcareous ridges, and five arches near the 

 internal edge of the corona. 



Five pairs of these muscles when acting together 

 protrude and retract the teeth ; when acting separately 

 they draw them to one side or to the other ; five pairs 

 separate the five teeth, five pairs shut them, and the 

 remaining five pairs work the bruising machine. The 

 masticated food passes through a short gullet into the 

 stomach, where it is digested, and the indigestible part 

 is carried by an intestine to the vent in the smaller 

 polar circle. 



The smaller polar circle is formed of ten triangular 

 plates, five are attached to the bands containing the feet 

 holes, and five to the intermediate bands. The last five 

 are perforated, and are the reproductive plates : the 

 other five are also perforated for the discharge of the 

 liquid that moves the tubular feet, and which, after 

 having circulated in the body, is no longer of use. In 

 five of these polar plates there are red specks, the rudi- 

 ments of eyes, the only organs of sense these creatures 



