STRUCTURE OF SERTULARIAN POLYPARY. 123 



in short, the greatest variety is exhibited throughout 

 the principal and subordinate parts of these elegant 

 zoophytes, which nothing but a copious series of ac- 

 curate delineations from luxuriant specimens could 

 illustrate, but which the reader may easily become 

 acquainted with by the assistance of a pocket lens, 

 while strolling upon the shore. 



The vigour and disposition of the tenant polyps 

 are sensibly modified by these provisions for security. 

 Instead of exhibiting the inactive languor of the naked 

 Hydrse, each little Sertularian polyp is seen to be 

 quick and lively in its motions. As if conscious of 

 danger, it lurks at the bottom of its receptacle ; it is 

 cautious of advance and precipitate in retreat. While 

 completely unfolded, all its organs suddenly collapse ; 

 it sinks within the cell in a moment, and crouching 

 still lower and lower, lies quiescent, until, the dreaded 

 peril over, it rises slowly as before, again to expand 

 itself. Now the whole is still, and apparently lifeless, 

 like a plant shorn of its flowers and foliage in the 

 winter-season it seems hastening to decay. Let it 

 remain undisturbed, and in a few moments it will be 

 covered by innumerable animated blossoms, issuing 

 forth from their cavities and spreading themselves out 

 in the light, and then, after seeking their enjoyments 

 in the plenitude of evolution, they again vanish in 

 instant retreat. 



The food of the Sertularian zoophytes seems to be 

 entirely derived from the microscopic organisms which 

 are contained in the surrounding water. Neverthe- 

 less this is a question which, simple as it might ap- 

 pear, is by no means satisfactorily determined, and it 



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