O. A. Merritt Hawkes 143^^ 



form for full spots, otherwise P larvae would have been found since 79(23) 

 is a heterozygous form although an 8 larva, being produced by the 

 union of an R8 and a P parent. The heterozygous nature of this R8 

 parent is shown by the number of the offspring — 40 P to 44 iS + R8, 

 approximately equal numbers of the recessive and the other types. The 

 heterozygous nature of these 8 types was proved by the P, 8 and R8 

 larvae which appeared in the subsequent generation (matings 92, 91, 

 84). 



One of the disadvantages in breeding animals with a short life is 

 that they are dead long before one knows their genetic content, as 

 judged by their progeny — on the other hand the families should be large 

 and hence certain judgments can be made as a result of a study of the 

 fraternity. 



The Fs generation: 



In this generation, for the first time, I did a large amount of fraternal 

 inbreeding, but the results, as far as the numbers were concerned, were 

 very poor, thirteen matings producing only 171 imagines. A much 

 smaller number of eggs were laid — in one case as few as 25 — but 

 this may have been due to the fact that I was also doing selective breeding 

 for a smaller type of moth. There was also a much reduced percentage 

 in the number of eggs hatched, which was as low as 25% and never 

 higher than 45 "Z^. In this generation only one mating (90) was not 

 fraternal, but that also was non-productive ; only 45 eggs were laid of 

 which 40 hatched, but in the end only one imago resulted. 



The fraternal matings (90, 93) produced only 8 and R8 offspring. 

 Three matings between brother and sister, both 8 (84, 85, 91), produced 

 all types of larvae. 



The Fs generation. 



This generation has been a failure for several reasons ; mice ate more 

 than two-thirds of the F^ cocoons, the moths that did emerge could not 

 be kept, on account of war conditions, at an adequate temperature, very 

 few eggs were laid, and finally the larvae grew so slowly in the cool 

 breeding room that many succumbed to disease. This generation pro- 

 duced one family (107), whose adult larvae all had the full complement 

 of spots. The larvae, numbering 23, were about to cocoon when they 

 died of cold. As the number of larvae which hatched was only 50, 

 the 23 which reached maturity were probably a good average lot, so 

 that one is justified in supposing that at last two parents with all the 



10—5 



