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 ^f 

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

 inhibits the appearance of the female secondary sexual characters. 



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

 stitutional formulae. 



HomlcM _ 

 females 



MFhhcc 



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

 numbers of homed and hornless ? s, (b) green ? s and yellow ? s in the 

 ratio of 1 : 3. 



As regards horns the parent $ was evidently heterozygous for H 

 and the parent J" 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 was left for some time in a cage with numerous c/s. The formula 

 of this ? is MFHhcc and if it paired first with a cT 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 c/* of the 

 same brood and gave approximately equal numbers of hornless yellow 

 and green 2 s. The parent ? being MFhhcc, the parent j" must have 

 been MMhhCc and the result is an equal number of yellow ?s MFhhCc 

 and green $ s MFhhcc. 



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

 brood l,^ave 11 horned ?s to 19 hornless ?s,and 11 green ?s to 



8 

 Journ. of Geu. iii 



