RADIARIES. 203 



surfaces, appear short, but being retractile, they 

 can be lengthened, and doubtless are used to 

 seize the animals that come in their way. What 

 can more strikingly indicate the contrivance and 

 design of an Intelligent Being than the structure 

 of these stellated animals by which they are 

 enabled to move in different directions, and to 

 secure their prey? 



The exterior envelope of the sea-urchins is 

 formed by two membranes, the one external 

 and thicker, and the other a very thin pellicle. 

 Between the membranes is a thick, solid, calca- 

 reous shell composed of a great number of 

 polygonal pieces of a fibrous tissue, evidently 

 immoveable, but not soldered during the growth 

 of the animal. The shell of the common species 1 

 if closely examined, when denuded of its spines 

 and other organs, will be found to be divided 

 into twenty longitudinal portions, ten of which 

 are covered with breast-shaped protuberances, 2 

 varying in size, which bear the spines, and ten 

 narrow ones perforated with a number of small 

 orifices, from which the tentacular suckers 

 emerge, which last Linne named alleys; 3 I 

 shall therefore call the spine-bearing ones groves. 

 These last are alternately wide and narrow, and 

 of a lanceolate form ; the wide ones having 

 six rows of the larger tubercles, and the narrow 



1 Echinus edulis. L. 2 PLATE III. FIG. 2. a. 



3 Ambulacra. Ibid. b. 



