Masao So and Yoshitaka Imai 321 



the present investigation the distinction between them was made without 

 marked difficulty. Some authors adopted the method of measurement 

 of the per cent, of pigmentation of the dorsal surface in classifying 

 the types of spotting. The writers, however, made the classification 

 depend upon the markings proper to the races. This method is much 

 simpler and gives very satisfactory results. 



In the present paper the dark-eyed white carrying a special factor 

 will be called "DarumaS" while for Miss Durham's dominant spotting, 

 or Little's spotting " Type A," the writers will use our word " Kasuri^" 



Material Used. 



Through the kindness of Mr Mito, a fancier in Tokyo, the material 

 used in the present investigation was mainly obtained. As these mice 

 belonged to the Japanese breed " Nankin," which has not only smaller 

 size of body but less resistance towards disease and unfavourable envi- 

 ronment compared to the European ones, the writers paid much 

 attention to improving its health by crossing with the common breed 

 of the latter. 



Mating: Self y. Piebald. 



The common piebald mice have long been used in breeding experi- 

 ments, and its recessive nature to the self-coloured is already proven by 

 many authors. The writers also repeated the experiment and secured 

 the same results. 



The young born in this sort of mating, however, were often neglected 

 and unrecorded in the present study, so the numbers contained in this 

 section are only a part of the results obtained in these matings. The 

 animals used in this cross were introduced from other fanciers ; those 

 who have not specially bred either the " Kasuri " or the " Daruma " race. 



When the normal piebalds are crossed with selfs the F^ animals are 

 all self-coloured. In the next generation, however, inbreeding of these 

 hybrids produces oflfspring consisting of self and#piebald in the pro- 

 portion of almost three to one. The actual numbers raised in the F^ 

 generation from this type of mating are represented in the following 

 table : 



Self Piebald Totals 



Observed ... 42 16 58 



Expected ... 43 -o 14-5 58 



1 " Daruma " or more correctly " Yuki-Daruma " means snow-man in English. The 

 name is given because the animal has a white coat contrasting with the black eyes which 

 Japanese children always give their snow-men. 



2 "Kasuri" means spotted. 



21—2 



