Control of Heredity: Eugenics 



267 



FIG. 99. COMMON COLORADO POTATO BEETLE, Leptinotarsa. a, normal 

 undecemlineata, b, the mutant augusto-vittata, c, the mutant melano thorax, 

 d, normal decemlineata, e, the mutant tortuosa, f, the mutant defecto- 

 punctata. (From Plate after Tower.) 



tance in the process of evolution so the question of their origin 

 is the greatest evolutionary problem of the present day. How 

 are such germinal variations produced ? 



There is some evidence that environmental changes of the 

 right sort acting upon germ plasm at the right stage may lead to 

 permanent modification of the hereditary organization. Extrin- 

 sic influences acting upon germ cells at the time of their matura- 

 tion divisions may lead to new distributions of chromosomes or 

 even to changes in the composition of individual chromosomes, 

 thus producing new hereditary types. Certain mutants of Oeno- 



