Other Kinds of Hybridizing 165 
petal. “The flush is transmitted independently of the length 
of the style or the size of the pollen grains, for it may be trans- 
ferred to the true short-styled or ‘thrum’ type. But when the 
flush is developed in plants which by gametic composition would 
be long-styled, the style does not pass through the anthers and 
the equal-styled condition is produced. Why the development 
of the yellow flush in these flowers should entail the reduction of 
the style, we cannot in any way suggest.” 
The discovery, that Primula follows the same law of inheri- 
tance as do other discontinuous variations, some of which are 
known to have appeared suddenly, furnishes an argument in 
favor of the view that the dimorphism in Primula owes its origin 
to discontinuous variation. Compared with the involved argu- 
ment by which Darwin attempts to show how natural selection 
has brought about the result, the mutation theory offers a much 
simpler and in my opinion a much more plausible interpretation. 
Reversal of Symmeiry 
In some species of snails the spiral of the shell turns to the 
right, in other species to the left. Occasionally in a right- 
handed species an individual that is left-handed is found, and 
there can be little doubt that such a form may suddenly arise. 
It is a discontinuous variation, but whether it is a mutation is 
not so clear, since the result may be due to an accidental shift- 
ing of the blastomeres on each other at the time when the 
unsymmetrical mesoblast cell is laid down. Nevertheless, the 
fact that entire species are characterized by the right- or the left- 
handed condition indicates that the factor that produces the one 
or the other result may at times be impressed on or arise in the 
egg, and be inherited. There are also species in which some 
individuals are right-handed, others left-handed. Here both 
possibilities seem to exist in the egg; but whether this can be 
referred to alternating dominance and recession, or to purely 
local conditions that arise during segmentation, is unknown. 
Somewhat similar conditions occur in the two kinds of chele 
of crabs, prawns, and other decapods; and perhaps the right- 
