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Protoplasm of different cells, showing foam structures. A— Pseudopod of a manne 

 rhizopod. The protoplasm only shows foam structure at the pomt of stimu- 

 lation B— Epidermic cell of lumbricus. C— Nerve fiber. D— Part of the cell 

 body of a ganglia cell. (A-C after Biitschli. D after Held.) 



