LIMITS OF HEREDITARY CONTROL 873 
the normal variability of the scutes in the banded region and in 
the individual bands, immediately following the variation data 
for the species, although it might appear to be more logical to 
complete the account of the conditions in the species before attack- 
ing that in the foetus sets. 
D. Fraternal correlation in the banded region as a whole; an 
index of the limits of hereditary control 
Having presented the facts of variation for the species, we are 
now in a position to investigate the conditions exhibited by the 
various ‘fraternities,’ which consist normally of ‘identical quad- 
ruplets,’ 2.e., of four individuals of the same sex enclosed in a com- 
mon chorionic vesicle. We have in our possession at the present 
time about thirty sets of foetuses in a stage of development suf- 
ficiently advanced to permit of the determination of sex and of the 
accurate enumeration of scutes. Of these some few are of especial 
value on account of their more or less atypical conditions; a few 
others are characterized by an atypical number of foetuses. 
There are, however, ten sets of each sex in which the number 
of foetuses, the arrangement of bands, etc., is sufficiently normal 
to permit of statistical treatment. These twenty sets furnish 
the material for the present study of correlation and the limits 
of hereditary control. The enumeration of scutes may be relied 
upon to be accurate, since they were all counted independently 
by both of the writers and all points of discrepancy carefully 
examined and settled according to mutual judgment. A full 
tabulation of the scute counts of the twenty fraternities is pre- 
sented in table 6. 
As in our previous papers the four foetuses are numbered as 
follows: 
Pair A { I. The lower individual of the right hand pair 
II. The upper individual of the right hand pair 
PairB  {III. The upper individual of the left hand pair 
\ IV. The lower individual of the left hand pair 
Since each of these sets of foetuses is derived from a single 
fertilized egg it should be possible to determine exactly to what 
