142 



Inheritance in Philosamia Hybrids 



more brother and sister matings, but these were not always possible, as 

 in each family the males tended to emerge some days before the females 

 and as the time during which the males will mate is only a few days 

 even when retarded by dark and cold, no matings could be effected ; 

 secondly, I did not wish at first to go contrary to the advice of ex- 

 perienced entomological breeders who were sure that inbreeding was 

 disastrous for moths. , 



The F^ generation. 



Ten families were reared but only three produced only S and R8 

 larvae, the results being as follows : 



Types of larvae ... P S RS 

 Mating QO RSxRS ... 8 5 



64 SxRS 

 76 RSxS 



12 

 15 



Totals 



36 



12 



The proportion of ^S* to RS is very different in this generation from that 

 in F3, but the numbers here are excessively small and the constitution is 

 doubtless different. 



Mating 64 had no fertile descendants and so the family came to an 

 end. Mating 75 is the descendant of mating 30 mentioned above. 

 Mating 60 is interesting as a demonstration that the RS form may be 

 either homo- or heterozygous as regards the character of full spots. 



The probability is that full spots are due to a series of unit characters, 

 which are linked to one another rather more closely than they are to 

 other characters. To demonstrate this would have required much more 

 space than was at my disposal. 



Mating 60 was produced by mating ^^ 25 (3) RS with $ 22 (7) RS; 

 a large number of eggs were laid, but there was great mortality at the 

 first three ecdyses. No P larvae were produced. Only 13 larvae spun 

 up, eight S and five RS, and of these few only ten moths emerged, viz. 

 1 S,S RS. If RS is a constantly heterozygous form, some P larvae would 

 be expected in the family. But as there was such a large mortality 

 all the P larvae might have died, especially if there was an extra large 

 death rate for the P type. Two members of this family, 60(5) and 

 60 (6), mated (mating 88, F^ generation), and produced all types of off- 

 spring, viz. S, RS and P, hence one of the grandparents was a hetero- 

 zygote. But, when another member of the family, 60 ( 1 0), mated with the 

 heterozygote 79 (23) S, in mating 90, only S and RS larvae were pro- 

 duced. This suggests that the other RS grandparent was a homozygous 



