MAYER: COLOR AND COLOR-PATTERNS. 275 
Thus the matter rested until 1879, when Fritz Muller brought out 
his well-known paper upon “ Ituna and Thyridia, 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 Avith an unalterable instinct which tells them 
exactly what they should and should not eat; so they may try 
experiments, and would then in all probability taste a few of the 
Heliconidae before finding out that they were unfit to eat. Muller 
then demonstrated that, if this supposition be true, it becomes a 
decided advantage to the various species of Heliconidae 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 butterfly 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; lienee, 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 Muller’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 : — 
