138 HEREDITARY CHARACTERS 



this result is, that the eggs became gradually accustomed to 

 the salt, and that the capacity to live in this new environ- 

 ment was due to a direct action upon the germ cells while in 

 the parent. Upon considering the matter more carefully, it 

 becomes evident that as the eggs were capable of develop- 

 ment as soon as maturation had occurred, that is, before the 

 death of the parent, the acquirements may have been made 

 entirely by the new generation, and certainly were not made 

 by parents, as they all died. 1 Again, there is apparently no 

 record in the experiment as to what proportion of eggs sur- 

 vived, and so the result was most likely due entirely to the 

 selection of an inborn variation occurring in a certain per- 

 centage of the eggs, which variation was towards tolerating 

 a certain amount of salinity. It may be in this case that 

 some of the ova, which of course were new individuals 

 capable of making acquirements on their own account, 

 acquired the capacity for living in a salt solution. The 

 selection of the inborn variation towards adaptation to the 

 new environment seems a more probable explanation. As 

 the parents were killed by the new environment, there is 

 not the slightest evidence that an acquired character was 

 transmitted, or that the effect of the environment upon the 

 parents produced any modification in the germ cells. 



It has been claimed that the results of certain experi- 

 ments with unicellular forms afford evidence for the trans- 

 mission of acquired characters. Certain pigment-producing 

 bacteria, when subjected to a temperature a little less than 

 that sufficient to kill them, lose the character of producing 

 pigment, and the immediately succeeding generations are 

 perfectly colourless. After a varying number of generations 

 the power of pigment production is regained. The number 

 of generations that do not produce pigment seems to be 

 proportionate to the severity of the treatment. 2 



1 As the great majority of Daphnice are reproduced parthenogenetically (see 

 p. 28), it is probable that the eggs must be regarded as separate individuals at 

 a very early stage. 



2 Adami, J. G., "An Address on Theories of Inheritance with Special Refer- 

 ence to an Inheritance of Acquired Conditions in Man," Brit. Med. Journ., 

 June 1, 1901. 



