ECHINIDM. 



28l 



sented here, supported and protected by a very complicated frame- 

 work, which has received the name of Aristotle's Lantern (Fig. 115). 

 Fig. 114 represents Echimis lividus, 

 with all its spines removed ; the 

 other shows the masticatory organs, 

 that is to say, Aristotle's Lantern. 

 To give the reader another idea of 

 the buccal organ in the sea-urchins 

 let him glance at a flattened form 

 from the southern seas, Clypeaster 

 rosaceus, represented in Figs. 116 and 

 117, an outline of the entire animal. 



The shape of Clypeaster rosaceus 

 is oval, straighter in front, and thick 

 and rounded at the edges. It is 

 more common and more largely dis- . 



tributed than perhaps any other allied species, and it is supplied 

 with four or six rows of ambulacral feet. 



It is not easy to understand why the dental framework of the 



Fig. 114. Buccal armature of Echinus 

 lividus. 





Fig. 115. Masticating apparatus of Echinus lividus. 





sea-urchin has been called Aristotle's Lantern, for this formidable 

 apparatus resembles the front view of a battery of cannon more than 

 a lantern. It consists of a series of pieces designated by the names 

 of compass, scythe, pyramid, and plumula, which it would serve no 

 useful purpose to describe in detail here. 



We have said that the mouth of the sea-urchin is quite out of 



