Characteristics, Origin, and History 9 



by Kishi (21 p. 481) and some other Japanese biologists. It 

 is their belief that the forms of movement acquired by the 

 individual as the result of confinement in narrow cages are 

 inherited. Thus centuries of subjection to the conditions 

 which Kishi has described (p. 6) finally resulted in a race of 

 mice which breed true to the dance movement. It is only 

 fair to add, although Kishi does not emphasize the fact, that 

 in all probability those individuals in which the dancing 

 tendency was most pronounced would naturally be selected 

 by the breeders who kept these animals as pets, and thus* 

 it would come about that select ional breeding would supple- 

 ment the inheritance of an acquired character. Few indeed 

 will be willing to accept this explanation of the origin of the 

 dancer so long as the inheritance of acquired characters 

 remains, as at present, unproved. 



Still another mode of origin of the mice is suggested by 

 the following facts. In 1893 Saint Loup (28 p. 85) advanced 

 the opinion that dancing individuals appear from time to 

 time among races of common mice. The peculiarity of 

 movement may be due, he thinks, to an accidental nervous 

 defect which possibly might be transmissible to the offspring 

 of the exceptional individual. Saint Loup for several months 

 had under observation a litter of common mice whose quick, 

 jerky, nervous movements of the head, continuous activity, 

 and rapid whirling closely resembled the characteristic move- 

 ments of the true dancers of China. He states that these 

 mice ran around in circles of from i to 20 cm. in diameter. 

 They turned in either direction, but more frequently to the 

 left, that is, anticlockwise. At intervals they ran in figure- 

 eights (oo ) as do the true dancers. According to Saint Loup 

 these exceptional individuals were healthy, active, tame, and 

 not markedly different in general intelligence from the or- 

 dinary mouse. One of these mice produced a litter of seven 



