218 



H. M. JOHNSON 



TABLE 2 



Record of Dog 1 



Discrimination between plain and striate fields 

 Width of each stripe on positive field: 3.902 mm. 

 Width of each stripe on negative field : 0. 104 mm. 

 Mean brightness of both fields: 6.2 candles per sq. meter 

 (Each test-object mounted in principal focus of lens, 399 mm. from nodal point) 



CONCLUSION 



Throughout the theories of the most important writers on 

 natural selection and sexual selection it is usually assumed either 

 expressly or implicitly that animals are visually sensitive to cer- 

 tain patterns or markings of the plumage or hair of their own 

 kind, as well as of their natural prey. Theories of protective 

 and warning coloration and marking are built on such an assump- 



