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Show 1903.] IN FANCY MICE AND RATS. 93 A line of inquiry is suggested by the miscellaneous constitution of F r W e 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 F0 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 resolution of characters had already begun ; and perhaps therefore 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 appear. In view of the facts I do not understand the meaning of Darbishire's statement that " the inheritance 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 FT x Fx f. * For further criticism of this statement see Castle and Allen (7). f As regards the waltzing character von Guaita's experiments agree with Darbishire's in showing that it was always recessive to the normal. No individual in Fj, or in families produced by crossing F T with the pure normal, waltzed. In Darbishire's experiments Fx X F, gave 8 waltzers in 37 offspring, indicating 1 in 4 as the probable average. D R X R is not recorded. From von Guaita's matings in the form D R X D R the totals of families were 117 normal and 21 waltzers made up as follows:- Normal. Waltzers. 36 8 14 2 25 7 41 2 1 2 117 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 numbers 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 D R x D R . i t is possible that the total of normals should really include some families which gave normals only. D R x R gave 18 normal and 10 waltzers distributed in families thus :- Normal. 3 3 10 2 18 10 Here the same paucity of recessives is noticeable. Von Guaita did not succeed in raising any offspring from extracted waltzers bred in f PI* S€- All that can be positively asserted is that the qualitative result is in full agreement with the Mendelian expectation based on the absence of waltzers in Fl5 and that it is not impossible that there may be the expected equality in number between D and R gametes produced by F,. Waltzers. 4 2 3 1 |