LIMITS OF HEREDITARY CONTROL 903 
Foetuses 1 and tv both show a completed splitting of the first 
band into two, thus producing ten bands; and they also lack the 
irregularity in the ninth band. 
Attention is called to the following points: 
1. All four members of the set show an extensive splitting of 
the first band. The splitting was predetermined in so far as 
the location within a certain band is concerned, but the extent 
or manner of its expression appear to have been beyond the limits 
of hereditary control. 
2. There was evidently a fairly rigid hereditary control in the 
matter of the various limits of the incomplete splittings, as one 
may judge by the facts that the two sides of foetus I are exactly 
identical and that six scutes constitute the marginal unsplit' region 
in every case where the splitting is incomplete. This would 
indicate a precision of hereditary control almost as remarkable 
as that noted in set 64. 
3. There is a pairing of foetuses on the basis of the extent of 
the splitting, pair A (1 and 1) showing an incomplete splitting, 
and pair B (im and Iv) a complete one. Pairing is again evident 
in the matter of the irregularity in the ninth band, pair A (1 and 
11) showing it, pair B (ar and tv) lacking it. 
4. The ‘three-to-one’ proportion appears again in that three 
individuals are bilaterally symmetrical and one is unilateral in 
the expression of the splitting process. 
Set 118 (Mother normal). This is the only set in our collec- 
tion where only one member of a set shows a band ‘abnormality.’ 
Foetuses I, 11 and Iv are normal. 
Foetus m1 shows a fusion of small extent between the first two 
bands, involving only three scutes at the left hand margin. 
The extent of the ‘abnormality’ is so slight that it seems scarcely 
worth while to discuss the possible bearings of thecondition. It 
would appear best to consider the case as one of incipient fusion, 
which may have arisen epigenetically in one of the four individ- 
uals. In the next generation it might have been inherited in a 
more pronounced form. There is, however, the alternative 
explanation which is developed in the discussion of the theoretical 
causes of pairing. 
JOURNAL OF MORPHOLOGY, VOL. 22, NO. 4 
