434 



GENERAL PHYSIOLOGY 



all organisms, and function as the indispensable condition of the 

 fertilisation of the egg-cell by the spermatozoon in animals as in 



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,' • o«. ^' 





■.■>i'- 



in 



Fig. 211. — Chemotaxis of Bacteria toward oxygen which is produced by ^^^ra-cells in the light. /, 

 Diatom evolving oxygen in sunlight and siurounded by Spirilla. II, Diatom half-shaded, 

 half -illuminated. The Bacteria have collected in the illuminated half, where oxygen is being 

 evolved. ///, An Alga-c&Yi. surrounded by Bacteria ; A, in the dai-k, B, in the light. (// and 

 /// after Engelmann.) 



plants. The spermatozoon seeks the ovum, and almost everywhere 

 in the living world is led in the right path by the chemotactic 

 action which the metabolic products of the egg-cell exert upon the 



