INHERITANCE OF MENTAL DEFECTS AND DISEASE 35 
oped. In the F, generation of a normal and a polydactylous 
person the dominant character varies from complete development 
to entire absence of visible somatic expression. In view of the 
frequency of such facts as these, and considering also the contin- 
uous variability in the manifestation of mental qualities in gen- 
eral, it is inadmissible to draw the conclusion that the mating of a 
normal person, even of sound stock, with a mental defective will 
be productive of mentally normal offspring. The supposition 
that matings of this sort are productive of offspring whose mental 
characters tend to be more or less intermediate between those of 
their parents, is one that is quite in accord with the large body of 
facts that has accumulated on the inheritance of mental traits. 
There are cases in which the mating of a person of good intelligence 
with a person of subnormal mentality has resulted in fairly intelli- 
gent offspring. but unions of this kind as a rule are not productive 
of happy results. Normal progeny from such matings may repre- 
sent cases where for some reason, the dominance of one parent is 
unusually complete. But the many cases in which the matings of 
normal and defective are productive of a variable degree of mental 
defect in the offspring may be to a considerable degree the result 
of imperfect and variable dominance. 
It has been generally assumed by a number of American work- 
ers that where mental defectives arise from such matings the 
apparently normal person was heterozygous. To account for the 
large number of defectives thus arising it has to be supposed that 
people heterozygous for mental defect are very common. In 
Goddard’s charts (Bull. Eugen. Rec. Off. No. 1) out of thirty 
matings of feeble-minded with presumably normal individuals all 
but two produced some feeble-minded offspring. In one of these 
(chart 6) three of the offspring, although they were marked nor- 
mal, had feeble-minded children. In the other family the only 
recorded mating among the presumably normal children was 
between an alcoholic woman and a man marked normal from 
another stock. This mating produced three normal and two 
feeble-minded children. 
It must be borne in mind, however, that the people marked 
