Experiments with other Mammals 113 



In the light of this analysis that Bateson has made of Crampe's 

 data, there can be little doubt that Mendel's law applies to many 

 at least of the phenomena of heredity in rats. This is made 

 highly probable by the recent results of Doncaster. He finds 

 that there are only two color types, brown (or gray) and black, and 

 only two color patterns in the colored-and-white individuals. 

 In addition there are albinos, but these may carry in a latent 

 condition either the uniform black or brown color, or the pie- 

 bald markings. Crosses between the black or the brown wild 

 rat with the albino may bring out the latent characters of the al- 

 binos. Doncaster points out that Crampe's work shows that 

 brown (gray) dominates black, and both brown and black 

 dominate white. The self or uniformly colored races i, 2, 6, 7 

 (and those having small white areas below) dominate the pie- 

 bald condition 3 and 5. 



Doncaster states that Crampe's brown forms i, 2, 3, 

 correspond exactly with the similar black forms 7, 6, 5, "but are 

 less simple to work with since they may contain recessive black." 

 He finds two varieties of type 6, one with much white and one 

 with very little. The latter belongs, in his opinion, to the uni- 

 form type. Crampe failed to make this deduction, so that one 

 of his forms was probably heterozygous. Evidence that the 

 inheritance in rats is Mendelian was found by Doncaster in a 

 number of the crosses made to test this question. 



Experiments with Cats 



Doncaster has brought together a number of records, ob- 

 tained from owners of pedigree cats, that show the color in- 

 heritance of certain breeds. He examined more especially the 

 question as to why tortoiseshell cats are nearly always females. 

 His conclusions, as will be seen, have an important bearing on 

 the problem of dominance in relation to sex. Tortoiseshell kit- 

 tens may be obtained in any of the following matings : 



(a) Tortoiseshell 9 by tortoiseshell $ 

 (6) Tortoiseshell 9 by black or blue $ 



