22 VIGNETTES FROM INVISIBLE LIFE. 



expanded leaflets, and carried round between the 

 double row of cilia towards the mouth. Here an im- 

 portant operation has to be performed. The mate- 

 rial collected is not all fit or required for food, and 

 consequently a sorting or selection is made before it 

 is admitted : some is sent down to the gizzard, there 

 to be more finely triturated and passed on as food ; 

 other is taken into the pug-mill, as the brick-making 

 machine is often called ; and the remainder rejected 

 as worthless. There is no stoppage of any one 

 operation for the performance of another : collecting, 

 sorting, grinding, and brick -making are all going 

 on simultaneously. You have before you a beau- 

 tiful piece of machinery, and hardly know which 

 part, of it to admire the most. Let us for a few 

 minutes watch the brick-making operation. We 

 see a few grains of matter spinning round, which 

 every moment is growing denser, acquiring consis- 

 tency and a rounded or conical form. In three 

 minutes it is finished and deposited on the outside, 

 where a film of gelatinous matter is already waiting 

 to receive it. Thus the first brick is formed. 

 Others follow in due course ; and soon a ring of 

 them is formed round the middle of the animal : 



