296 The Inheritance of Wing -Colour in Lepidoptera 



female being sometimes melanic and sometimes type, the ratio is very 

 far from the expectation. In fact, there are 63 "/^ of melanic instead of 

 50 °/^, which is rather closer to a ratio of 3 : 1 than to equality. In order 

 to find out what the significance of this unusual ratio might be, a number 

 of matings were made, the offspring from which are recorded in the 

 following table : 



Melanic (heterozygous for type) x Type. 

 First Broods. 



Imagines 



In these experiments it seems clear that the factor for melanism 

 behaves normally, producing as many black insects as type. As however 

 the numbers were not very large, those insects which emerged in July 

 1920 were paired, so as to obtain eggs from which a second brood could 

 be raised. This was accomplished and the numerous larvae were fed 

 first on lilac and then on privet, but it happened that there was a very 

 severe frost in December, which caused the leaves of all the privet 

 shrubs to fall. For various reasons no attempt was made to give the 

 larvae, which were nearly full grown, any other food, and less than half of 

 them succeeded in spinning cocoons. Of these only about half pupated 

 completely and they emerged in May 1921, about a month after those of 

 the first broods, which had hibernated in the pupal state. The result of 

 these matings is given in the table on p. 297. 



A glance shows that although the numbers are very small, the ratio 

 ot melanic to type is different from that given by the first broods in the 

 previous table, and in this the experiments resemble those of Hamling 

 and of Harris. When it is remembered that the mortality in the second 

 broods was over 75°/^, the explanation of this difference between the 

 first and second broods does not seem very far to seek. The inference 

 is that the mortality was selective, more melanic insects being able to 



