FACTS AND FACTORS OF DEVELOPMENT 53 



flexes are seen in the movements of bacteria, 

 protozoa and many higher animals and plants 

 as well as in movements of spermatozoa, the 

 movements of the protoplasm in egg cells and 

 embryonic cells, the movements of cells and 



19* 19* 



26* f 38 



10 25~ 



FIG. 19. REACTIONS OF Paramecium TO HEAT AND COLD. At 

 a the infusoria are uniformly distributed in a trough, both 

 ends of which have a temperature of 19; at 6 the infusoria 

 are shown collected at the cooler end of the trough; at c they 

 have collected at the warmer end of the trough. (From Jen- 

 nings, after Mendelssohn.) 



