LANTERN OF ARISTOTLE. 225 



There are five long teeth, each of which is enclosed 

 in a triangular bony piece (fig. 6 c, d), that, for the 

 sake of brevity, we will call jaws. The five jaws are 

 united together by various muscles, so as to form 

 a pentagonal pyramid, having its apex in contact 

 with the oral orifice of the shell ; while its base is 

 connected with several bony levers by means of 

 numerous muscles provided for the movements of 

 the whole. When the five jaws are fixed together in 

 their natural position, they form a five- sided conical 

 mass, aptly enough compared by Aristotle to a 

 lantern, and frequently described by modern writers 

 under the name of the " lantern of Aristotle." The 

 whole of this complicated machinery is suspended by 

 muscles from a framework fixed in the interior of the 

 shell, and may often be picked up upon the beach, or, 

 still better, exposed in situ in a dead Echinus, by 

 those who would examine closely this wonderful piece 

 of mechanism. 



The Echini, in the structure of their ovarian appa- 

 ratus, exhibit, if possible, greater simplicity of ar- 

 rangement than even the Star-fishes described in a 

 preceding chapter. The ovaria are five delicate mem- 

 branous bags, quite distinct from each other, which 

 open externally by as many delicate tubes, or oviducts, 

 as we may term them. The apertures through which 

 the eggs escape are easily seen upon the outer surface 

 of the shell, placed around the opening opposite to 

 that of the mouth, and are at once recognizable, not 

 merely by their size, but from the circumstance of 

 each perforation being situated in a distinct oval plate 

 of the shell, distinguished by zoological writers as the 



L 5 



