Malformations are more common in illegitimate children than in legitimate and more common in alcoholic mothers; there is an unfavorable environment of poverty in both cases, added to in the latter and usually in the former by the injurious action of the alcohol.
The more extensive malformations have no effect on heredity, because the subjects of them are incapable of procreation.

The malformations which arise from the accidents of pregnancy and which are compatible with a perfectly normal germ are in the nature of acquired characteristics and are not inherited.

Those malformations, however, which are due to qualities in the germinal material itself are inherited, and certain of them with remarkable persistence.

There are instances in which the slight malformation consisting in an excess of fingers or toes has persisted through many generations.

It may occasionally lapse in a generation to reappear later.