ness
as it existed in a French family. The inheritance is obviously
Mendelian: no affected persons are produced by unaffected parents,
although their own brothers or sisters or one parent may have been
affected. The pedigree gives the history of 2,040 persons, all
descended from one affected individual. Of these 135 were known to
have been affected, and all were children of affected parentage. Of
the total number of progeny of affected persons mated with normals,
130 were reported as affected and 242 as unaffected.

[Illustration: FIG. 16.--Two family histories showing split
foot. (From "Treasury of Human Inheritance.")]

We may consider next the hereditary history of some forms of nervous
defect, the exact nature of the causes of which can be less definitely
stated than in all of the preceding instances of defect. Fig. 20 gives
a brief history of the heredity of Huntington's chorea--a form of
insanity which here resulted in the death of all but one of the
affected persons in the first four generations; the fifth generation
is the present and is incomplete. Although the matings were with
normals in every case, yet in four of the eight marriages all of the
offspring were affected. From one affected male 23 affected persons
descended in four generations and their multiplication is still going
on. There can be no doubt as to the unfitness of marriage into such a
family.

[Illustration: FIG. 18.--Family history showing a form of
night blindness. Character of matings incompletely known.
(Data from Bordley.)]

A very complete family history showing deaf-mutism is given in Fig.
21. It cannot be said that in every case here the defect is innate,
i. e., hereditary, and it is not known that the cause of the defect
was the same in every family concerned, for deaf-mutism may result
from several different causes. In most cases in this history, however,
the defect behaves like a Mendelian dominant. In certain other cases
it is clearly known to follow the Mendelian formula. Such pedigrees
as this show how dangerous it is to marry into a family in which this
defect exists.

[Illustration: FIG. 19.--Family history showing a form of
night blindness. (Condensed form of Nettleship's data.)]

Goddard has recently published several family histories showing
feeble-mindedness. One of the most significant of these--significant
both socially and eugenically--is summarized here in Fig. 22. Of this
Goddard writ