T44 LIFE HISTORIES OF THE PROTOZOA, 
laria have a many chambered shell like those of the Polytha- 
mia. 
While the Foraminifera live mostly at the bottom of the sea 
(some, however, occurring between tide marks) on stones and sea- 
weeds, creeping over sand and mud by means of their pseudopods, 
the marine Radiolaria for the most part float with outstretched 
pseudopods on the surface of the sea. They occur in countless 
numbers, but are usually so small that until 1858 they had been 
almost entirely overlooked by naturalists. The compound, or 80- 
cial forms, such as Collosphera, are nearly an inch in diameter, 
while most of the simple species cannot be seen with the naked 
eye. The Polycystina occur fossil in abundance at Barbadoes, 
Richmond, Va., and the Nicobar islands. 
Development. So far as is known Amoeba multiplies its kind only 
by the simplest mode of reproduction known, that of self-divis- 
ion. The following figure (133), copied from Heckel, represents 
Fig. 133. 
Amoeba sphrrococcus. 
highly magnified, Ameba spherococcus, a fresh-water species WE 
out a contractile vesicle, in the process of fission ; at is is a 
encysted Ameeba in its “resting stage.” It now consists er 
spherical lump of protoplasm (d), in which is a nucleus (e) a 
its nucleolus (b) and the whole surrounded by 3 cyst or a 
membrane (a). It breaks the cell-wall and becomes free a 
