892 H. H. NEWMAN AND J. THOMAS PATTERSON 
itary basis. It would seem to be profitless to attempt any detailed 
analysis of the conditions in the sets tabulated, but there are 
some points worth study that have not been mentioned. 
Every case in which two or more individuals show a scute 
‘abnormality’ is almost undoubtedly a case involving some phase 
of hereditary control, for on the basis of chance there would be 
very few sets more than one individual of which would have a 
double scute. 
In concluding this account of the hereditary control of double 
scutes attention might be called to the fact that in this connection 
we have excellent material for testing Galton’s ‘‘minutest bio- 
logical unit capable of hereditary transmission.’? Whether or not 
these minute pecularities of the scutes are directly inherited from 
the immediate parents we cannot at present determine, but we 
are certain that the conditions are blastogenic in the sense that 
they are predetermined in the fertilized egg. If this be the equiv- 
alent of hereditary transmission we may rightly claim to have 
found just the sort of unit that Galton was looking for. It seems 
unlikely that any smaller unit could be predetermined. 
(2). Three-hair type of scute. In only one set of foetuses (set 
135) have we found that peculiar condition described as a possible 
discontinuous variation or mutation. Although we are unable 
to count the hair primordia in the foetuses, we are confident that 
the great majority of them are of the three-hair type. This 
assumption is justified by the fact that the scutes have the same 
narrow appearance that is seen in adults in which the three-hair 
type prevails, and by the additional circumstance that we have 
never found an individual with over 600 scutes in which the three- 
hair type of scute did not largely predominate. As an additional 
piece of evidence in favor of the idea that the condition in question 
is a mutation, it seems highly probable that it is inherited in the 
exclusive fashion and is dominant. If we suppose that the foe- 
tuses show a blend between the mother, an individual with 573 
scutes, and the unknown father, it would necessitate the positing 
of a male parent with a scute number far in excess of any we have 
found to occur in the species. That the lower scute numbers, 
which are made up from shells showing comparatively few three- 
