Lay f 
LIMITS OF HEREDITARY CONTROL 879 
if we were certain of the origin of each pair of twins, for the twins 
have doubtless been much modified by post-natal environmental 
experience. 
Incidentally it may be noted that the male sets exhibit a much 
higher absolute variability than the females sets, a fact which 
will be brought into discussion in a subsequent connection. 
Perhaps a more equitable comparison between human twins 
and the armadillo sets would be instituted if we were to consider 
the quadruplet set as consisting of two pairs of twins. Accord- 
ing to this method of comparison the difference between the two 
species is greatly increased, for the average of the forty pairs of 
armadillos is only 0.27 per cent, while that of the seven pairs of 
human twins is 1.62 per cent. 
In concluding the present account of the strength of hereditary 
control as it appears to be exercised in the case of the total num- 
ber of scutes in the banded region, it should be mentioned that 
further investigations now in progress, dealing with other regions 
of the armor and with certain dimensional variates, indicate 
TABLE 8 
Showing the standard deviation of each of the sets of foetuses and indicating the 
comparative variability of male and female sets with respect to the total 
number of scutes in the nine bands. 
FEMALE SETS MALE SETS 
STANDARD COEFFICIENT - | STANDARD COEFFICIENT 
SET DEVIATION OF VARIATION SET DEVIATION | OF VARIATION 
(IN SCUTES) (IN PER CENT) (IN SCUTES) (IN PER CENT) 
DePee bm cere 2.38 0.438 La ee 2.48 0.48 
A Fa, See es 3.69 0.66 As a, oa a 0.5 0.08 
95 25 0.45 Peer SP ho le. 25386 1.10 
eee a came ard he 15 0.26 D2 arene ono 0.63 
OOM relat 72 2.16 0.38 LUGS eee 3.46 0.61 
UGE es ee. 2.59 0.46 A. sees een 2.38 0.43 
121 2.86 0.50 (20 Se eet 5.70 0.99 
122 1.92 0.35 1s 7: eye oe 3 Sea 4.02 0.72 
123 1.87 0.34 LBS ee the! 6.36 | 1.04 
pe ech, 2.85 1.06 TSS eaebys ate. 1.56 0:28 
