LIVING SUBSTANCE 



77 



alga Eiiastrum (Fig. 19, a) represents such a cell with lobate 

 processes, and the ganglion-cells in the central nervous system 



FIG. 18. a Egg-cell from the ovary of a sea-urchin. (After Hertwig.) 6, Epidermis-cells from 



the frog. 



of man, the brain and spinal cord, which give origin to the nerve - 

 fibres, possess constant processes which appear exactly like the 



FIG. 19. , Euastrum, a unicellular alga from the group of the Desmidiacece. 

 (After Haeckel.) b, Ganglion-cell from the human spinal cord. (After 

 Gegenbaur.) z, Cell-body ; n, nerve-process (axis-cylinder process). 



pseudopodia of many rhizopod cells (Fig. 19, &). 

 Other cells, the ciliated cells, have upon their sur- 



