Toyarna, On certain characteristics of the Silk-worm etc. I >( ),"> 



outer zygotic 



appearance composition 



F, D X R D DR 



F! R X D R DR. 



In the case where the female is recessive, the resulting F t eggs 

 will be all R in their appearance and in the reversed mating all D. 

 Zygotically, however, they are both the same; namely DR in their 

 composition. 



Moths derived from F t D, or R eggs whose zygotic composition 

 is DR when mated inter se will give the following combination in F 2 . 

 DR X DR = DD -|- 2RD -f- RR. 



Considered zygotically, therefore, F 2 eggs will be of three kinds, 

 DD, DR, and RR but to outward appearance they are all D, no R 

 ones, since all the females have the composition DR in which D 

 only is an active factor in determining the character of the egg 

 which is formed in the body of the female before fertilization 

 takes place, provided that dominancy is perfect. If this is not the 

 case, there would be produced some batches in which both D and 

 R forms are mixed together. 



In spite of being all D in F 2 , the moths derived from F 2 worms 

 have a different composition; namely DD, DR, and RR. As we 

 have no means of distinguishing them from one another by outward 

 appearance, we should expect to have a random mating between 

 them. They will give the following combination in F 3 . 



Outward Zygotic 



appearance composition 



1. ?DD X cTDD D DD 



2. $ DD X cf DR D ( DD + DR ) 



3. $ DD X cf RR D DR 



4. $ DR X cT DD D (DD + DK) 



5. $ DR X cf DR D (DD-fDR-fRR) 



6. $ DR X d* RR D DR + RR 



7. $ RR X c? DD R DR 



8. $RRXd*DR R (DR + RR) 



9. $ RR ; cf RR R RR 



By the reasoning above stated, those females with the composi- 

 tion of DD or DR will give all D F 3 eggs and those with RR all 

 R eggs, in spite of their males being DD, DR or RR. 



Hence F 3 eggs derived from F 2 D eggs should be D and R, 

 that is to say, some matings will produce all D batches, others 

 all R eggs, and if all the moths were reared the proportion of D 

 and R batches produced in F 3 will be 2D: 1R. 



In the F 3 D series above quoted, two (matings Nos. 5 and 6) 

 will disintegrate into R and D forms as there are RR females, 

 while the remaining four in which the zygotic compositions of 

 females are DD or DR, the F 4 eggs will be all D. Hence F of 



