HIS THEORY OF HEREDITY 113 



Two remarkable^instances, one from the animal, 

 the other from the vegetable kingdom, may be 

 cited before passing to some further considerations. 

 There is a curious kind of mouse, known as the 

 Japanese " waltzing mouse," which gets its name 

 from the fact that it will spend hours in the day 

 chasing round and round after its own tail. It is 

 known that this curious habit is the result of a 

 malformation of the semicircular canals, passages 

 connected with the internal ear and having to do 

 with the balancing power of the possessor. Experi- 

 ments were made by breeding " waltzers " with 

 normal mice, the result showing that the malfor- 

 mation in question functions as a unit in compar- 

 ison with the normal condition and that it behaves 

 as a recessive. Thus, to make things quite clear, 

 the offspring of a " waltzer " and a normal mouse 

 is always normal, but in the next generation 

 " waltzers " reappear. 



Readers of Darwin's books will be aware that 

 he devoted much attention to the question of the 

 two kinds of primroses which exist in nature in 

 about equal numbers. In one of these varieties, 

 which is called " thrum," the anthers are in the 

 top of the tube and the style is short. In the other, 

 or " pin-eyed," the anthers are at the point of 

 contraction of the tube and the style is long. 

 These two characters also behave as Mendelian 

 units. The " thrum " is the dominant form, and 

 long-styled plants, being recessive, never produce 

 short-styled, unless they have been fertilized from 

 a flower of the other variety. As Bateson points 

 out, this fact goes a long way towards disposing of 



