POLYPI. 171 



reous wall of the future cell. Towards the base 

 of this rudimental cell, the gelatinous substance 

 in the interior may be perceived to become more 

 consistent and opaque at a particular point ; 

 from this dull spot within the cell, short straight 

 tentacula begin to bud, extending upwards in 

 the direction of the future aperture. The gela- 

 tinous spot, from which the tentacula originated, 

 assumes the vermiform appearance of the body 

 of a polype ; and we may distinctly perceive 

 the bundles of fibres which connect its head with 

 the base of the cell. The structure of the polype 

 is perfected by the addition of a closed capsule ; 

 and when it is first detected protruding from the 

 cell, it possesses all the parts of an adult polype, 

 and vibrates the cilia of its tentacula with as 

 much regularity and velocity as at any future 

 period. Before the polype is capable of protrud- 

 ing from the aperture of the first cell, the upper 

 part of the cell has already extended outwards 

 to form the rudiment of a second : and so on, in 

 succession, till the whole structure is completed. 

 The tentacula of polypi are exquisitely sen- 

 sible, and are frequently seen, either singly or 

 altogether, bending their extremities towards 

 the mouth, when any minute floating body 

 comes in contact with them. When a polype 

 is expanded, a constant current of water is 

 observed to take place, directed towards the 

 mouth. These currents are never produced by 

 the motions of the tentacula themselves ; l)ut 



