

Heredity and the Origin of Variations. 147 



tions just in the particular direction in which they are 

 wanted. The question is Are they transmitted? and if 

 so, how ? 



Let us begin with the protozoa. Dr. Dallinger made 

 some interesting experiments on monads. They extended 

 over seven years, and were directed towards ascertaining 

 whether these minute organisms could be gradually ac- 

 climatized to a temperature higher than that which is 

 normal to them. Commencing at 60 Fahr., the first 

 four months were occupied in raising the temperature 

 10 without altering the life-history. When the temperature 

 of 73 was reached, an adverse influence appeared to be 

 exerted on the vitality and productiveness of the organism. 

 The temperature being left constant for two months, they 

 regained their full vigour, and by gradual stages of increase 

 78 was reached in five months more. Again, a long pause 

 was necessary, and during the period of adaptation a 

 marked development of vacuoles, or internal watery spaces, 

 was noticed, on the disappearance of which it was possible 

 to raise the temperature higher. Thus by a series of 

 advances, with periods of rest between, a temperature of 

 158 Fahr. was reached. It was estimated that the re- 

 search extended over half a million generations. Here, 

 then, these monads became gradually acclimatized to a 

 temperature more than double that to which their ancestors 

 had been accustomed to a temperature which brought 

 rapid death to their unmodified relatives. 



Now, in such observations it is impossible to exclude 

 elimination. It is probable that there were numbers of 

 monads which were unable to accommodate themselves to 

 the changed conditions, and were therefore eliminated. 

 But in any case, the fact remains that the survivors had, 

 in half a million generations, acquired a power of existing 

 at a temperature to which no individual in its single life 

 could become acclimatized. Here, then, we have the 

 hereditary transmission of a faculty. But the organisms 

 experimented on were protozoa. In them there is no dis- 

 tinction between germ-cell and body-cell. Multiplication 



