320 Spotti7ig in Mice and their Genetic Behaviour 



in mice and in guinea-pigs it varies so much, both in amount as well as 

 in type, that there exists hardly any definite, well-recognized type such 

 as hooding in rats. Furthermore, it has often been stated that the 

 variation of the spotting in these animals not only occurs in a continu- 

 ous series of gradations, but also extends from the nearly self-coloured 

 animals to one having a slightly pigmented coat. 



In mice, besides the recessive spotting just stated above, there was 

 recognized the existence of a so-called dominant spotting, as well as a 

 dark-eyed white which carried a special factor. 



Miss Durham (1908) seems to be the first author who took these 

 special race's for use in breeding experiments. Crossing such a dark-eyed 

 white animal to the self-coloured one she obtained the so-called dominant 

 piebald, which, however, she failed to distinguish phenotypically from 

 the ordinary recessive one. In that paper she stated incidentally that 

 when such a dominant piebald is mated with itself the result may be 

 expected to be spotted and self-coloured young in a ratio of three to one ; 

 or, in other words, such a spotting is transmitted as a dominant Mendelian 

 unit to the self, which, in turn, dominates over the ordinary, spotting. 

 Actually, however, the case is somewhat complicated, as will be seen in 

 the following sections. As to the significance of the dark-eyed white 

 she did not pay much attention to it. 



Morgan (1909) and Hagedoorn (1912) seem to have taken these 

 types in their breeding experiments, but the evidence obtained by them 

 was not enough to be convincing. 



With these works already known the writers took up the experiments 

 in 1915 hoping, if possible, to understand their real nature. But, at the 

 close of that year. Little's important paper (1915) was published, in 

 which he gave an account in full of this subject. He detected another 

 independent factor for the coat pattern, in addition to those for self and 

 common piebald. In the following year Detlefsen (1916) made similar 

 observations with special emphasis on the pink-eyed white carrying 

 the colour factor (= pink-eyed "Daruma"). Recently, Little (1917) 

 attempted to find out the relation of the lethal action between the 

 factors of black-eyed white and yellow coloured. 



The results obtained by the writers agree, on the whole, with those 

 reported by Little and by Detlefsen, but in the present paper they hope 

 to give some additional facts on this pattern inheritance in mice. 



All the authors cited above failed to separate phenotypically the 

 two types of spotting and recorded them together in the mixed progeny, 

 though they are entirely different genetically one from the other. In 



