1903.] IN FANCY MICE AND RATS, 93 



A line of inquiry is suggested by the miscellaneous constitution 

 of Fj. We have seen that all members of F, are not alike, and it 

 is not impossible that the greys from families which give no blacks 

 or yellows may be different in constitution from greys in families 

 which gave one or the other. If the individuality of the several 

 parents of F^ were given, this possiblity could be examined. The 

 fact that an original waltzer was giving off yellow or black gametes 

 might be an indication that i-esolution of characters had already 

 begun ; and perhaps thei'ef ore the F, from different families, though 

 alike grey, may be in some measure heterogeneous. In these cases 

 it is most important that each individual parent and its offspring- 

 should be separately traceable. 



It is not impossible that some light on these questions could be 

 obtained by noting the sexes in which the several forms appeax. 



In view of the facts I do not understand the meaning of 

 Darbishire's statement that " the inhei*itance of eye-colour is not 

 in accordance with Mendel's results." * So far as the experiments 

 are yet recorded, the behaviour of the eye-colour is typically 

 Mendelian, and follows Mendelian expectation in its simplest form. 

 The occurrence of albinos is similarly Mendelian, one albino in 

 four being plainly indicated as the average from F^ x F^ t. 



* For further criticism of this statement see Castle and Allen (7). 



t As regards the waltzing character von Guaita's experiments agree with Darbi- 

 shire's in showing that it was always recessive to the normal. No individual in F,, 

 or in families produced by crossing F;^ with the pure normal, waltzed. In Darbishire's 

 experiments F^ X F, gave S waltzers in 37 ofFsprina:, indicating 1 in 4 as the probable 

 average. DRx R is not recorded. From von Guaita's matings in the form DR X DR 

 the totals of families were 117 normal and 21 waltzers made up as follows : — 



117 21 



There is therefore a large excess of normals over the expected 3 to 1. This is 

 possibly due to the delicacy of the waltzers, which are certainly much more difficult to 

 rear than normals are. The small nmnbers in von Guaita's litters make it very likely 

 that many were lost before such a character as this could be determined. On the 

 other hand, we have to bear in mind that as the presence of waltzers is here the only 

 proof that the matings were in the form DRxDR, it is possible that the total of 

 normals should really include some families which gave normals only. 



DRXR gave 18 normal and 10 waltzers distributed in families thus :— 



18 10 



Here the same paucity of recessives is noticeable. 



Von Guaita did not succeed in raising any offspring from extracted waltzers bred 



All that can be positivelj' asserted is that the qualitative result is in full agree- 

 ment with the Mendelian expectation based on the absence of waltzers in F^, and 

 that it is not impossible that there may be the expected equality in number between 

 D and R gametes produced by F,. 



