LIMITS OF HEREDITARY CONTROL 913 
position, nutrition, etc. That the environmental factor cannot 
be seriously considered is shown when particular cases are exam- 
ined. What kind of an environmental stimulus, for example, 
could operate to produce such a definitely localized, minute 
peculiarity as the double scutes in the individuals of sets 121 and 
123? One could hardly imagine that a slight difference in the 
amount or character of the maternal nutriment would produce 
such a condition, nor could any mechanical factor, such as posi- 
tion, pressure or contact with the amnion, be held accountable for 
so definitely localized a character occurring in several individuals. 
Again, in the matter of atypical band arrangements, it would 
appear equally absurd to attribute resemblances or differences to 
environmental factors. Consider, for example, the conditions 
in set 64. Here the region of incomplete splitting is so definitely 
localized and involves so fixed a number of scutes that one would 
have to posit some kind of environmental influence which would 
be able to cover just so many scutes and place itself just so far 
from the margin in every case. It would also be necessary to 
explain why two of the four individuals should show the effects 
of the influence bilaterally and why the other two should show it 
unilaterally. 
These and many other cases that might be examined point to 
the untenability of the position taken by the proponents of the 
efficacy of environmental factors, and strongly fortify the position 
here taken, that the characters dealt with are purely of blastogenic 
origin. We conclude then that we have without question made an 
advance in the direction of determining the limits of hereditary 
control. We have shown with what degree of exactness the num- 
bers of certain integral variates, the scutes, may be predetermined 
and how much room is allowed for the play of epigenetic factors. 
We have demonstrated that the alignment of scutes into bands 
is very largely controlled by mechanical factors. We have indi- 
cated the degree of exactness with which certain ‘abnormalities’ 
may be hereditarily controlled, and how small a biological unit is 
capable of predetermination. 
One cannot but be impressed, however, with the diversity of 
conditions seen in the different sets. In some of the normal sets 
