THE LIFE OF THE SIMPLEST ANIMALS 17 
fine threads interlace when they touch each other, thus — 
forming a sort of protoplasmic network outside of the shell. 
In some cases there is a complete layer of protoplasm— 
part of the body protoplasm of the protozoan —surround- 
Fic. 10.—Polystomella strigillata, one of the Globigerine.—After Max ScuuLTze. 
ing the cell externally. The Radiolaria, whose shells are 
made of silica, possess also a perforated membranous sac 
called the central capsule, which lies imbedded in the 
protoplasm, dividing it into two portions, one within and 
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