2. _Datura._ As for the evidence on _Datura_, I must refer the reader again to the experiments set forth in our Report. The phenomena obey the ordinary Mendelian rules with accuracy. There are (as almost always where discontinuous variation is concerned) occasional cases of “mosaics,” a phenomenon which has nothing to do with “ancestry.” 3. _Colours of Rats and Mice._ Professor Weldon reserves his collection of evidence on this subject for the last. In it we reach an indisputable contribution to the discussion--a reference to Crampe’s papers, which together constitute without doubt the best evidence yet published, respecting colour-heredity in an animal. So far as I have discovered, the only previous reference to these memoirs is that of Ritzema Bos[133], who alludes to them in a consideration of the alleged deterioration due to in-breeding. [133] _Biol. Cblt._ XIV. 1894, p. 79. Now Crampe through a long period of years made an exhaustive study of the peculiarities of the colour-forms of Rats, white, black, grey and their piebalds, as exhibited in Heredity. Till the appearance of Professor Weldon’s article Crampe’s work was unknown to me, and all students of Heredity owe him a debt for putting it into general circulation. My attention had however been called by Dr Correns to the interesting results obtained by von Guaita, experimenting with crosses originally made between albino _mice_ and piebald Japanese waltzing mice. This paper also gives full details of an elaborate investigation admirably carried out and recorded. In the light of modern knowledge both these two researches furnish material of the most convincing character demonstrating the Mendelian principles. It would be a useful task to go over the evidence they contain and rearrange it in illustration of the laws now perceived. To do this here is manifestly impossible, and it must suffice to point out that the albino is a simple recessive in both cases (the waltzing character in mice being also a recessive), and that the “wild grey” form is one of the commonest heterozygotes--there appearing, like the yellow cotyledon-colour of peas, _in either of two capacities_, i.e. as a pure form, or as the heterozygote form of one or more combinations[134]. [134] The various “contradictions” which Professor Weldon suggests exist between Crampe, von Guaita and Colladon can almost certainly be explained by this circumstance. For Professor Weldon “wild-coloured” mice, however produced, are “wild-coloured” mice and no more (see Introduction).