446 THE AQUARIAN NATURALIST. 



crusted with stones and shells, or decorated with 

 parasitical, though ornamental plumes of corallines, 

 that not unfrequently form valuable additions to the 

 stock of the aquarium. 



When we consider the fixed and immoveable con- 

 dition of one of these helpless creatures, and its abso- 

 lute deprivation of all prehensile instruments adapted 

 to seize prey, it is by no means evident at first sight 

 how it is able to subsist, or secure a supply of nourish- 

 ment adequate to its support : neither is the structure 

 of the mouth itself, nor the strange position which it 

 occupies, at all calculated to lessen the surprise of the 

 naturalist who enters upon a consideration of this part 

 of their oeconomy. The mouth, in fact,is quite destitute 

 of lips, or other extensible parts, and situated, not at 

 the exterior of the body, but at the very bottom of a 

 capacious bag enclosed in the interior of the creature. 

 It is obvious, then, that whatever materials are used 

 as aliment must be brought into the body with the 

 water required for respiration ; but, even when thus 

 introduced, the process by which they are conveyed 

 to the mouth still requires explanation. A truly 

 miraculous apparatus is provided for this purpose. 

 The whole surface of the respiratory chamber is 

 covered over with multitudes of vibratile and closely- 

 set cilia, arranged in millions, which by their united 

 action cause currents in the water, all of which flow 

 in continuous streams directly towards the mouth. 

 It is sometimes possible, in very young and trans- 

 lucent specimens, by the aid of a good microscope, 

 to witness the magnificent scene afforded by these 

 cilia when in vigorous action : 



