J. C. F. Fryer 



109 



(/s and the fact that the segregating character is structural seem to 

 be strongly in favour of the correctness of the result. 



As a working hypothesis for the explanation of the experiments as 

 a whole it may be supposed that horns are caused by the presence of 

 a factor H, in the absence of which, represented by h, the insect is 

 hornless. Similarly as yellow colouration appears to be dominant over 

 green it may be due to a factor G, in the absence of which, c, the insect 

 is green. Then if the sex factors are represented by MM in the J* 

 and MF in the % it must be supposed that the combination MM 

 inhibits the appeai'ance of the female secondary sexual characters. 



Under this scheme the (/s and $s must have the following con- 

 stitutional formulae. 



Brood 1 arose from a horned green % and contained (a) about equal 

 numbers of horned and hornless % s, (h) green % s and yellow J s in the 

 ratio of 1 : 3. 



As regards horns the parent J was evidently heterozygous for H 

 and the parent (/ contained hh, lacking H altogether. 



The colour problem is more difficult and can only be explained by 

 supposing that the $ paired more than once, which was possible, since 

 it wa.s left for some time in a cage with numerous (/"s. The formula 

 of this $ is MFHhcc and if it paired first with a (/" of constitution 

 MMhhCc and then with one MMhhCC an excess of yellow offspring 

 would be produced. 



Brood 3. A hornless green $ from brood 1 paired with a ^ of the 

 same brood and gave approximately equal numbers of hornless yellow 

 and green 2 s. The parent $ being MFhhcc, the parent ^ must have 

 been MMIiliCc and the result is an equal number of yellow ^s MFhhCc 

 and green $ s MFhhcc. 



Brood 5. A horned green ? fi-om brood 1, paired with a J' of 

 brood 1, gave 11 horned $s to 19 hornless $s, and 11 green ?s to 



Juiirn. of Gen. in 8 



