406 V. THE NATURE OF EVOLUTINN 



on the flower is to cause a characteristic change in the colour. The 

 oldest known example is tulip break due to an aphis-transmitted mosaic 

 virus. Another common virus variegation occurs in the flowers of 

 wallflowers and stocks and other cruciferous plants (80). These ex- 

 amples should be regarded as mutations due to viruses rather than as 

 virus-diseases. 



Many breeders believe that domestic animals will sometimes breed 

 the young resembling on some point to the male animal which is not 

 the true father of the young but with which the mother animal was 

 once crossed, a phenomenon called telegony. This phenomenon is, of 

 course, never consistent with the modern theory of genetics, and ac- 

 cordingly it has been dismissed as a mere bigotry. Nevertheless, this 

 appears possible according to the writer's concept. 



It has been well established that males of cancer strains of mice 

 may transfer the virus-like agent capable of producing the cancer at 

 the time of copulation to infect females of either susceptible or rela- 

 tively resistant strains and that these infected females may propagate 

 and pass the agent to their progeny (81). If this is caused by "infec- 

 tion", not by the transmission of the pattern through the germ cell to 

 the progeny, such a female mouse may be able to transfer the character 

 of the male to the young of another male. In case where the sperm 

 of a male after the fertilization developed in the body of a female into 

 the foetus, the influence of a male pattern upon the female would 

 probably be far more striking. Moreover, it may not be quite im- 

 possible that every married couple tends to become Jack and Jill after 

 a prolonged cohabitation not only through the mental connection but 

 through virus-like agents. 



