212 FUNCTIONS AND INSTINCTS. 



sidered, and the nature of its food, and the force 

 necessary to prepare it for digestion, it was 

 evidently requisite that it should be defended by 

 a crust sufficient to afford a support, and give 

 effect to its powerful oral apparatus, and yet 

 light enough to yield to the efforts of its motive 

 powers; but as this crust, from its composition 

 and nature, was liable to be crushed by a very 

 slight pressure, it required further means of 

 defence, and with these its Almighty and 

 Beneficent Creator has amply provided it, by 

 covering it, like a hedge-hog, with innumerable 

 spines, varying in length, and capable of various 

 movements. The long ones, when erected, 

 defend it on all sides, both from the attack of 

 enemies and from the effects of accidental pres- 

 sure, and we may conjecture that when the 

 longer ones are couched to answer any particular 

 purpose, the short ones may come into play, and 

 assist in keeping any pressure from the crust. 

 Perhaps, as in the hedge-hog, the ordinary 

 posture of the longer spines is couchant, and 

 they are only erected when the animal is in 

 motion or under alarm. 



The wonderful apparatus which closes the 

 mouth of the common or typical sea-urchin, 1 

 is another and striking proof that Creative 

 Wisdom employs diversified means to attain a 

 common end, the nutrition of the animal. 



1 Echinus edulis. 



