518 S. O. MAST 



after the opposite reversion has been induced by an increase 

 in temperature. Similar results were obtained in observations 

 on the effect of light. Thus, it is evident, that the temperature 

 or the illumination required to produce reversion in orientation 

 in given colonies varies greatly. It should be emphasized here 

 that the effect of light and temperature are opposite, i.e., an in- 

 crease in temperature produces the same effect as a decrease in 

 light and vice versa. 



DISCUSSION 



The experimental results presented in the preceding pages 

 indicate that reduction in alkalinity, increase in anesthetics, 

 increase in temperature, and decrease in illumination, all have the 

 same effect on the sense of orientation in Spondylomorum. They 

 also indicate that the same change in the sense of orientation may 

 occur without any appreciable change in the environment. It 

 is consequently probable that re\'ersion in orientation is due 

 to some specific change in the physiological processes of the organ- 

 ism which can be induced by changes in any one of the environ- 

 mental factors mentioned, i.e., alkalis, anesthetics, temperature, 

 and light. What these processes are is not known. They may 

 involve electrical tension and polarization or permeability or 

 absorption. 



We have demonstrated that reversion depends upon the time- 

 rate of change of effective factors in the environment. This. 

 howe^'er, does not prove that reversion is dependent upon the 

 time-rate of change in the physiological processes involved rather 

 than upon the state of the physiological processes as such, for 

 we have also demonstrated that reversion induced by a given 

 environmental condition is rarely, if ever, permanent. That is, 

 if negative colonies are put into a solution containing the proper 

 amount of chloroform, they become positive, but they usually 

 remain positive only a few minutes and then become negative 

 again. This indicates that there is rapid adjustment on the part 

 of the organism to the new environmental condition. The fact, 

 therefore, that reversion is not induced if the effective factors in 

 the environment are slowly changed, may be due to adjustment 



