H. Onslow 



235 



In the three prece<ling faniiliea tho yellowH have iilwiiyH hcrii in 

 excesH. Tho result of eoinbining them* thnu' faiiiili»*H is to maki' the 

 ratio of the receanive f«)nu to the dominant (JS : :\2 (jmt ct-nt.), a sonn*- 

 what K»wer |)n>j>*>rtion t»f yellows than in 1(1 A. In Fi^^ 4 thr pro|Hnti<»n 

 of yellows to hybrids wa.s about •V():54(|)er cent.), but the evidence dti ivid 

 from the four large families of alxmt XO inserts rarh, is undoublrdly mon* 

 valuabK> than that derived tVom a nuinlHT of small on«'s. Furtli«T the 

 offspring fnmi all pairings of the ty|>e PR x RH have been combined in 

 one curve. Fig. 9, which resembles the fivi* preceding curves in most 

 essential pi^ints : and results in a nitio of 41 : 50 (per cent.). But jls 

 a matter of fact there are not sut!icient data from which to draw a definite 

 conclusion, especially as no confirmatory evidence is forthcoming from 

 the other crosses. 



Fig. 9. Curve showing frequency distribution of the orange and yellow colour- 

 values of the offspring from all the hybrid {lutca x gross.) x lutea families 

 shown in Figs. 4, 5, 6, 7, and 8. 



(d) Hybrid {lutea x gross.) x hybrid {lutea x gross.). 



The frequency distribution shown in Fig. 10 is composed of a number 

 of small families of this cross, none of which were large enough to be 

 treated by themselves. 



If the heterozygous yellows, which are often distinguishable from the 

 white type by their pale yellow colour, were really to form a distinct class 

 to themselves there should be three maxima in Fig. 10. Clearly there 

 are only two, showing that the pale yellow heterozygous class passes 

 by insensible changes into the pure white DD class with an orange value 

 of less than 08. It should however be carefully noted in Fig. 22 that 

 there are 48 insects or 24 per cent, with a colour value of 08 and 



