LESSON 32.] NUTRITION IN THE ECHINODERMA. 



Ill 



powerful teeth, called the " Lantern of Aristotle," for the comminu- 

 tion of the food (Fig. 188). It is a singular fact that, in this Class, 

 the number five, or its multiples, constantly meet us : Jive i&ys,Jive 

 teeth ; ten coscal appendages, and so on. In the Class Acalepha, 

 FIG. 1ST. FIG. 188. 



The Lantern of Aristotle. 

 , The Teeth. 

 &, The Alveolar pro- 



Nutrimental organs, Echinus. 



c, Hooks for the attach- 

 ment of muscles. 



four and its multiples are as constantly found ; the tentacles are four 

 in number or eight ; and this principle is constant in these two classes. 



532. The teeth, (Fig. 188, a) are three-sided prisms, dense at the 

 lower, pointed extremity, softer at the base, with their inner edge 

 sharp and fit for cutting; they are each implanted in a larger trian- 

 gular pyramid (5), two sides of which are in close apposition with 

 opposite sides of the adjoining pyramids, and are transversely grooved, 

 like a file. 



A further view of two of these teeth, in apposition by the alveo- 

 lar processes, is given (Fig. 189). The upper, soft portion of the 

 teeth is shown at a ; the terminal, hardened 

 part at b ; the alveolus at c. The secretion 

 of some simple salivary follicles assist in com- 

 pleting the mastication of the food. These 

 teeth are put in motion by a series of well- 

 developed muscles, said (by Valentin) to con- 

 sist of the striped fibre. 



533. In the cavity of the lantern is the 

 pharynx, which is divided by five longitudinal 

 folds ; the salivary coeca are placed in its im- 

 mediate neighborhood. A slender oesophagus 



FIG. 189. 



Two of the Teeth of Echi- 

 nus, natural size. 



