LIMITS OF HEREDITARY CONTROL 897 
44-51, it would be a perfect example of bilateral symmetry; (b) 
in shell no. 21, in which band 1 has 59 scutes, the splits are in 
scutes 8-13 and 46-52—here again a change of one point on the 
right side would make a bilaterally symmetrical ‘abnormality’; 
and (c) in shell no. 13 there are 63 scutes in band 1, and the splits 
are in scutes 4-16 and 48-59— a close approximation to sym- 
metry. These conditions remind one of Wilder’s results in dupli- 
cate twins, already referred to in the introduction. (2) The 
second point to be emphasized is this, that although the atypical 
variations in the bands show a marked degree of regularity in 
occurring so frequently in the first and second bands, yet they 
display a great diversity in the fact that scarcely any two of them 
are exactly alike. This diversity for the species is striking when 
considered in the light of the fact that in 1768 specimens examined 
but two sets of coincidences have been found, and these occur in 
the simplest type of ‘abnormality.’ Since many of the shells 
upon which these data were taken are from the same locality it 
is not improbable that some of these cases are either brothers or 
sisters, and not coincidences. The fact that only two sets of 
these supposed cases of coincidences, and these of the simplest 
type (very slight fusions), have been found in 1768 individuals 
will serve to emphasize the importance of fraternal correlation 
as brought out in a subsequent section of the paper. 
D. Hereditary control in connection with band ‘abnormalities’ 
Considering the comparative rarity of band ‘abnormalities’ 
in the species we have been fortunate to secure a collection of 
sets of foetuses, among which appear examples of practically all 
of the types of malformation described above. As in the case 
of meristic variation in the normal scutes and in the matter of 
double scutes the precision of hereditary control is much more 
marked in some cases than in others; in some the conditions are 
fairly simple and in others highly complex. The sets are described 
in detail and discussed separately, in so far as the special condi- 
tions of each case are involved. The general significance of many 
of the observations can be discussed to advantage only after all 
