224 THE AQUARIAN NATURALIST. 



This enables them more readily to secure their food 

 with the aid of the numerous suckers in the vicinity 

 of their mouth, which, when once they are fixed, never 

 let go their hold till the animal is brought within the 

 action of their powerful jaws." 



We really should be glad if some of our readers 

 could throw a little light upon this part of the eco- 

 nomy of the Sea-urchins; it is a very interesting 

 subject for investigation. 



The jaws of the Echinus, indeed, are as curiously 

 formed as any other part of their structure. Their 

 mouth is a simple orifice through which the points of 

 five sharp teeth are seen to protrude. These teeth 

 obviously perform the duty of incisors, and from their 

 sharpness and extreme density are well calculated to 

 break the hard substances said to be employed as 

 food. The points of such incisor teeth, although of 

 enamel-like hardness, would nevertheless be speedily 

 worn away by the constant attrition to which they 

 are necessarily subjected, were there not some pro- 

 vision made to ensure their perpetual renewal : like 

 the incisor teeth of rodent quadrupeds, they are there- 

 fore continually growing up behind as fast as they are 

 worn away in front, and are thus always preserved 

 sharp and fit for use. In order to allow of such an 

 arrangement, as well as to provide for the movements 

 of the teeth, jaws are provided, which are situated in 

 the interior of the shell, and these jaws, from their 

 great complexity and unique structure, form perhaps 

 the most admirable masticating instrument met with 

 in the animal kingdom. The entire apparatus, re- 

 moved from the shell, consists of the following parts. 



