166 Experimental Zoology 
handedness and left-handedness in man belongs to the same 
category. It is also known that in man all of the viscera may be 
in a reversed position, and the aortic arch also. 
Lang has bred together some left-handed snails of the right- 
handed species, Helix pomatia. They produced only right- 
handed individuals. These were also inbred and produced only 
right-handed young. It is evident that this new character is 
not inherited in this instance and also that it does not behave 
as a recessive to the right-handed condition, for, if it did so, it 
would have reappeared in the grandchildren. 
Physical difficulties seem to interfere with the union of the 
sinestral individuals of Helix with dextral forms, so that as a rule 
the sinestrals are precluded from breeding, unless by chance 
they meet one of their own kind; but even if this occurs all the 
offspring will be dextral again, and no opportunity exists to per- 
petuate the new race. If, however, in other species the left- 
handed condition should be heritable, such individuals might, if 
once started, establish a variety alongside of the parent forms, 
although the two forms might be prevented by their difference in 
structure from pairing. That the left-handed condition must 
sometimes be inherited is shown by the existence of species of 
this sort. 
Conclusions regarding Mendelian Inheritance 
The examples of discontinuous inheritance given in the pre- 
ceding chapters make it clear that Mendel’s law accounts in 
many cases for the results, and is therefore an invaluable acqui- 
sition to our method of interpretation; yet in some other cases 
it is evident that the inheritance is not strictly Mendelian. Used 
with discretion the law may still unlock many problems, but if 
attempts are made to force it to interpret cases that do not 
belong to its proper field of action, especially in regard to dissocia- 
tion in the germ-cells, harm rather than good may temporarily 
result. 
The most striking exceptions are those recorded by Standfuss and by de Vries 
(cenothera). Other cases involve blending, etc. 
