THE SIELTCEBTA. lol 



into four rounded segments, not unlike the flower of the 

 heart' s-ease, supposing the fifth petal to be obsolete. The 

 entire margin of this flower-like disk is set with fine 

 vibratile cilia, the current produced by which runs uni- 

 formly in one direction. Thus there is a strong and 

 rapid set of water around the edge of the disk, following 

 all its irregularities of outline, and carrying with it the 

 floating particles of matter, which are drawn into the 

 stream. At every circumvolution of this current, however, 

 as its particles arrive in succession at one particular point, 

 viz., the great depression between the two uppermost 

 petals, a portion of these escape from the revolving 

 direction, and pass ofl" in a line along the summit of the 

 face towards the front, till they merge in a curious little 

 cup-shaped cavity, seated on what we may call the chin. 



This tiny cup is the mould in which the bricks are 

 made, one by one as they are wanted for use. The 

 hemispherical LQterior is ciliated, and hence the contents 

 are maintained in rapid rotation. These contents are the 

 atoms of sedimentary and similar matter, which have 

 been gradually accumulated in the progress of the ciliary 

 current ; and these, by the rotation within the cup becom- 

 ing consolidated, probably also with the aid of a viscid 

 secretion elaborated for the purpose, form a globular 

 pellet, which as soon as made is deposited, by a sudden 

 inflexion of the animal, on the edge of the tube or case, at 

 the exact spot where it is wanted. The entire process of 

 making and depositing a pellet occupies about three 

 minutea 



