202 
itary tendency for twinning, others are 
frequently met with in which, while 
there may be a record of many indi- 
divuals in several generations, only one 
pair of twins appears. In these in- 
stances the twins sometimes seem to 
be biovular, sometimes uniovular. Such 
family histories may indicate that while 
twinning is in some way hereditary in 
most instances, it may nevertheless at 
times appear sporadically. The most 
probable inference to be drawn from 
this fact would seem to be that the 
ability to produce twins is_ possibly 
common to all strains and that the fre- 
quency of twin births in different lines 
is merely relative. It is not likely, on 
the one hand, that strains will be found 
in which twins never occur nor, on the 
other hand, in which there is nothing 
but twins. But that such causes as 
may tend toward twin production” are 
more constant or react more effectually 
in some lines than in others seems 
evident. That one of the factors com- 
monly involved in the case of both 
uniovular and biovular twinning is he- 
reditary seems to be well established, 
although it cannot as yet be stated 
12 There is not space to discuss these causes in detail. 
A slight transient hyper-acidity of the uterine 
important influencing factor (biovular twins). 
The Journal 
of Heredity 
whether or not the method of trans- 
mission is Mendelian. 
SOLUTION NOT IMPOSSIBLE 
In the foregoing discussion an attempt 
is made to give the “‘setting’’ of a con- 
crete problem in the study of human 
heredity for which purpose the question 
of twinning is selected. The obstacles 
that are met in attempting to solve this 
problem are found to be of such a nature 
as to prevent a quick arrival at final 
conclusions, but they are not such as 
to discourage the hope that a definite 
solution of the problem may be ob- 
tained. Before such a _ solution is 
reached, however, a number of inci- 
dental, and perhaps unforeseen, ques- 
tions must be disposed of. These 
questions often call for excursions into 
somewhat remote fields of investigation, 
but this fact instead of detracting from 
the interest of the study or the urgency 
for its prosecution, adds materially to 
both. It is only through the careful 
evaluation and correlation of all these 
contributary data that entirely satis- 
factory conclusions can be hoped for. 
Many obstetricians consider age an 
fluids has been suggested as a factor favoring the production of uniovular twins. 
Laws to Restrict Miscegenation 
Twenty-eight states have laws or 
constitutional provisions forbidding the 
intermarriage of negroes and white 
persons, while twenty States have no 
laws on the subject, according to Albert 
Ernest Jenks, who reviews the legislation 
in the American Journal of Sociology 
(March, 1916). In ten States, bills 
introduced in the legislatures and aimed 
at forbidding negro and white marriages 
were defeated in 1913, largely through 
the activity of the National Association 
for the Advancement of Colored People. 
This association announces that it 
does not favor intermarriage, but objects 
to such legislation on the ground that it 
is ineffective and discriminatory, that 
it leads to the degradation of negro 
women, and ‘for the physical reason 
that to prohibit such intermarriage 
would be publicly to acknowledge that 
black blood is a physical taint, some- 
thing no self-respecting colored man 
and woman can be asked to admit.” 
Prof. Jenks points out that in the States 
which have laws, these laws differ 
widely in the interpretation placed on 
the word ‘‘negro.”’ “If effectual legal 
barriers against negro-white amalgama- 
tion are desirable,’ he concludes, “‘they 
should perfectly agree as to the legal 
and racial status of the so-called 
‘negro,’ and miscegenation of every 
form and every instance between negro 
and white persons must be made a 
felony in every American State.”’ 
