106 IXTKODUCTIOX TO COXCHOLOGY. 



with violet. Peculiar in his habitat and location, this kind 

 of mollusk is apparently restricted to the ILeandrina pliri/gia 

 and the shores of the Eed Sea. 



The growth of the Magilus presents n kind of negative 

 anakgy with that of the Xaidilus. The inhabitant of each 

 advances to the outer porch of his cell by the aid of a 

 relaxing muscle, and the mode of their operation is curiously 

 adapted to existing circumstances. The former, in order 

 to sustain the increasing pressure of liis coral home, tills 

 up the empty portions of liis shell with a sohd substance ; 

 the latter, ha^dug a watery element to contend with, increases 

 the buoyancy of his habitation by several light partitions. 

 If this plan was adopted by the Magilus, his outer walls 

 would probably be crushed by the increasing growth of 

 cord; if the XautUus fiUed up his vacaut shell after the 

 manner of the Magilus, he would be unable to move from 

 place to place, or to ascend from his haunts in the fathom- 

 less abyss. 



Li both, the instinct of the auimal is rendered subser- 

 vient to the purpose for which it is designed ; — the one to 

 glide in its mimic boat, unharmed amid the terrors of the 

 deep; the other to lead a hermit life, imbedded within 

 blocks of coral, for the perfecting of wliich innumerable 

 workmen are continually employed. 



