MAYER: COLOR AND COLOR-PATTERNS. 201 



Thus the matter rested until 1879, when Fritz Miiller brought out 

 his well-known paper upon " Itiina and Th>'ridia, a remarkable 

 example of mimicry," in which he showed that both of these genera 

 are protected, yet they mimic each other. He also showed that this 

 mimicry might be due to Natural Selection brought about in the 

 following manner. It is possible that young birds, upon leaving the 

 nest, are not furnished with an unalterable instinct which tells them 

 exactly what the}' should and should not eat; so they niay try 

 experiments, and would then in all probability taste a few of the 

 Ileliconidae before finding out that they were unfit to eat. Miiller 

 then demonstrated that, if this supposition be true, it becomes a 

 decided advantage to the various species of Ileliconidae to resemble 

 one another. His reasoning was as follows : Let it be supposed 

 that the young and inexperienced birds of a region must destroy 

 1,200 specimens of any distasteful species of butterfiy before it 

 becomes recognized as such, and let us assume further that there are 

 in existence 2,000 specimens of species A, and 10,000 of species B ; 

 then, if these species are different in appearance, each will lose 1,200 

 individuals, but if they resemble each other so closely that they can- 

 not be distinguished apart, the loss will be divided pro rata between 

 them, and A will lose 200, and B 1,000 ; therefore A saves 1,000 or 

 50% and B saves only 200 or 2% of the total number of individuals 

 in the species ; hence, while the relative numbers of the two species 

 are as 1 to 5, the relative advantage derived from the resemblance 

 is as 25 to 1. 



Blackiston and Alexander ('84) have given a complete mathe- 

 matical statement of Miiller's law, and have come to the conclusion 

 that, if the number of individuals destroyed is small compared with 

 the number constituting the species, the relative advantage is 

 inversely as the square of the original numbers ; but if the number 

 destroyed is large compared with the original number, the ratio of 

 advantage is much greater than the inverse squares of the original 

 numbers. Their deduction may be briefly stated as follows: — 



