LIMITS OF HEREDITARY CONTROL 883 
ATYPICAL VARIATION IN THE INDIVIDUAL ELEMENTS AND IN 
THE BANDS 
A. Scute ‘abnormalities’ in the species; their distribution and 
. frequency 
(1). Double scutes. In the individual scutes and in the bands 
certain so-called ‘abnormalities’ frequently occur, and while 
these may be but the expression of teratological phenomena, yet 
we believe that some of them at least are the result of more deeply 
seated factors and have a real phylogenetic significance, and con- 
sequently are worthy of consideration in a paper on variation and 
heredity. We shall speak of them as atypical variations. 
The atypical variation of the scutes is expressed in at least 
three different ways, one of the most frequent of which we shall 
designate as the ‘double scute.’ In this type two contiguous 
primary scutes are fused along their adjacent sides, and the double 
structure thus formed has five or six hairs at the free or posterior 
end (figs. 6a, 7a, 8a). Evidently there is a suppression of two 
or three hairs consequent upon this union. All stages of fusion 
have been observed in our material, and in the figures just 
referred to is seen a series of three, taken from one specimen 
showing different degrees of the process. The nature of the origin 
of these double scutes is made clear when the region affected is 
examined from the under side, where the double bony element 
is always clearly expressed (figs. 6b, 7b, 8b). Sometimes the 
bony elements are of equal size and occupy the full width of the 
band, but more frequently one of the plates is greatly reduced, 
as if there had been a tendency to crowd it out (fig. 8b). 
The double scutes occur in about ten per cent of the animals— 
or to be more exact, in a total of 516 individuals examined for this 
particular point 51 showed double scutes. Ordinarily there is 
but one of these to an animal, but four exceptions to this have 
been found, as follows: one with four double scutes, one with 
three, and two with two each. 
For the purpose of locating exactly the various scutes, we have 
chosen to begin their enumeration always on the left margin of 
the band. Thus scute ‘10’ of band 5 would be the tenth scute 
