PRIMARY ORGANIZATION OF LIVING MATTER 



29 



demonstrated in the skin of the salamander, are conspicuous in Volvox, 

 and have been described for many kinds of animal cells (Fig. 20). In 

 plants, cell bridges are usually present, the fine protoplasmic filaments 

 passing through minute pores in the cell walls. Presumably these 

 l)ridges are lines of communication between cells, but they are not 





Fig. 20. — Iiiteicellular l)riclges; left, highly- thicketied human ei)itlieliiiiii; right, ik r. iiinuon. 

 {Courtesy of General Biological Supply Hous,.) 



essential, since cells in contact with one another are capable of passing 

 litiuids or electric currents from one to another without such connections. 



References 



Shari', L. ^^^ An introduction to Cytology. 3d Ed. McGraw-Hill Book C*oni- 



pany, Inc. (Chap. II; details of parts of cells, Chaps. III-VII.) 



Wilson, E. B. The Cell in Development and Heredity. 3d Ed. The Macmillan 



Company. (Chap. I.) 



