OCEAN LIFE. 81 



mechanism the Echinus glides along to browse the corralines, 

 and other Zoophytes, which clothe the rocky reef or sea-girt 

 precipice. The creature's mouth is carried next the ground ; it 

 is a circular orifice, surrounded with a fleshy ring, through which 

 protrude five sharp crystalline teeth, whose points all meeting in 

 the centre serve to nibble off the substances employed as nutri- 

 ment, and thus, without apparent instruments of sense, such as 

 belong to higher animals, and unpossessed of limbs except its 

 spines and suckers, the sea urchin marches on with ease, in 

 situations where, apparently, no footing could be found, and lives 

 a life of indolent security, encased in solid armor and beset with 

 spines, compared with which, the bristles of the hedge-hog are a 

 poor protection. Such being the general habits of the Echinidce, 

 our next inquiries must relate to their construction, and perhaps 

 we are already prepared to expect that this must offer many 

 features worthy of remark. 



" The shell, or dense calcareous crust, that seems to enclose the 

 animal, is really placed internally, for although it contains the 

 viscera appointed for nutrition, all the living flesh, the real sub- 

 stance of the creature is external to it. Let this fact be well remem- 

 bered if we would appreciate the analogies which still ally those 

 globe-like beings to the star-fishes, and through them to the 

 polyps. 



" t The shell, in the fresh animal, is covered over with a thin 

 fleshy skin filled with calcareous points. This skin is fibrous 

 and contractile, being, in truth, the representative of the soft 

 fleshy covering that encases all the branches of an JEnorinite, 

 and which in Asterias moves the rays and spines. It is in fact 

 the animal itself; it forms the shell within and likewise wields 

 the external organs, the stiff prickles, when employed as instru- 

 ments of locomotion. Though more distinctly muscular than in 

 inferior zoophytes, and consequently capable of contracting more 

 energetically, it contains the power of separating earthy matter 

 from the sea wherewith it moulds the shell that gives it shape, 

 and also constructs the countless spines that stud the outer sur- 

 face of the body, all of which are built by slow precipitation of 

 calcareous particles secreted by the living skin itself. Imme- 

 diately beneath the living tegument is placed the shell, itself a 



