888 H. H. NEWMAN AND J. THOMAS PATTERSON 
the hair groups are larger than in the more highly differentiated 
region like that of the bands, is prima facie evidence that here 
the direction of evolution is from the four-hair to the three-hair 
type, with a consequent increase in the total number of scutes. 
These high numbered specimens with their many scutes of the 
three-hair type are of further interest because they are probably 
to be regarded as mutations, in the sense that they represent dis- 
continuous variations. This in part can be made clear by an 
inspection of table 1. At the lower end of the series therein rep- 
resented the specimens occur with a frequency sufficient to be 
explained on the basis of an ordinary fluctuating variability, and 
this is also true of the other end of the series up to the specimen 
with 596 scutes; but beyond this point specimens are of rare occur- 
rence and consequently are separated by wide gaps. However, 
neither the rarity of their occurrence nor their wide separation 
is sufficient to place such specimens in the category of mutations, 
because there is always the possibility that a larger number of 
the species would furnish variates enough to fill up the gaps. If 
we would therefore explain these as saltations we must look to 
another source of information, namely, to their behavior in inherit- 
ance. This topic will receive attention in a succeeding section. 
B. Hereditary control in connection with scute ‘abnormalities’ 
(1). Double scutes. Attention has been called to the com- 
parative rarity of double scutes in the species and to the fact that 
in only a very few cases do double elements fall in the same place 
inthesame band. Itisrarely the case even that the same general 
region of a band of more than two specimens shows the peculiarity 
in question. When, therefore, we find in as many as three out 
of four members of a set of foetuses a double scute in almost 
precisely the same locality, we are forced to the conviction that 
even these elements, which might be defined in the words of Galton 
as ‘the minutest biological units,’ are predetermined in the undi- 
vided germ cell. 
Two sets of foetuses show the conditions most clearly and 
they are described in detail below: 
