x] MIMICRY AND VARIATION 129 



obscura is what is to be looked for in a population mating 

 at random. This case of the polymorphic Pseudacraea 

 eurytus is one of the greatest interest, but it would be 

 hazardous to draw any far-reaching deductions from 

 such facts as are known at present. When the genetics 

 of the various typical forms and of the intermediates 

 has been worked out it will be disappointing if it does 

 not throw clear and important light on these problems) 

 of mimetic resemblance. 



As the result of modern experimental breeding 

 work it is recognised that an intermediate form between 

 two definite varieties may be so because it is hetero- 

 zygous for a factor for which one variety is homozygous 

 and which is lacking in the other — because it has 

 received from only one parent what the two typical 

 varieties receive from both parents or from neither. 

 Its germ cells, however, are such as are produced by 

 the two typical forms, and the intermediate cannot be 

 regarded as a stage in the evolution of one variety from 

 the other. In these cases of mimicry the existence of 

 intermediate forms does not entail the deduction that 

 they have played a part in the evolution of one pattern 

 from another under the influence of a given model. 

 It is quite possible that the new mimetic pattern 

 appeared suddenly as a sport and that the intermediates 

 arose when the new form bred with that which was 

 already in existence. But before we are acquainted 

 with the genetic relationships between the various 

 forms, both types and intermediates, speculation as to 

 their origin must remain comparatively worthless. 



