FRESH-WATER RHIZOPODS 155 



varies from the three-hundredth to the one hundred 

 and twenty-fifth of an inch. The shell seen under 

 very high powers shows a minutely hexagonal struc- 

 ture, and is translucent. These hexagons are said to 

 be the twelve-thousandth of an inch across ! Not 

 only this, but they are hollow, like so many 

 saucers. 



The arcella is found in standing water. It feeds 

 on algae and other vegetable matter, and is frequently 

 found on the surfaces of submerged plants. 



When it grows too large for its shell, it comes out 

 and secretes material for a new covering. Sometimes 

 the old shell and the new one are found together ; 

 the former is generally much darker than the new 

 one. Until the new home is quite complete the 

 creature lives partly in one and partly in the other. 

 When, however, the old home is finally forsaken, it 

 splits. 



Small cell-like bodies have been observed by 

 Biitschli to escape from the mouth of the shell, and 

 to assume the movements and appearance of the 

 amoeba. But he was not able to ascertain if they 

 were the young brood of the arcella. Our informa- 

 tion respecting this creature is far from complete, so 

 that another opportunity awaits the microscopist. 



Fig. 45 represents another class of Rhizopods 

 known as Cyphoderia (Gk. knphos, curved ; deros, the 

 neck). These creatures have a retort-shaped shell, 

 which is transparent and generally coloured, and 

 which is intrinsic. Under high magnification this 



