900 H. H. NEWMAN AND J. THOMAS: PATTERSON 
the two types is quite impartial in so far as their frequency is 
concerned, for, out of the possible eight lateral halves of the four 
foetuses, four are occupied by each type. It would appear from 
this that each was equally strongly predetermined; but the exer- 
cise of hereditary control in the distribution of the two types 
among the four foetuses is somewhat haphazard and reminds one 
strongly of a pure chance combination of two elements selected 
in pairs, like, for example, the Mendelian ratio of F 2’s, D-2Dr-r. 
4, Apart from the ‘secondary’ fusion of one of the split half 
bands with the scapular shield, the members of the natural pair 
B (11 and tv) are strikingly identical. Evidently hereditary con- 
trol within the pair is more accurate than in the whole set. The 
explanation of this condition must be discussed in the subsequent 
section on pairing. 
Set 96 (Mother normal). This case is somewhat simpler than - 
the last in that it involves only one type of ‘abnormality,’ namely 
a simple fusion of the first two bands. We have decided to call 
the condition a fusion, because, including the two which are 
united, there are only nine bands. ‘The strictly marginal charac- 
ter of the band unions would also serve to indicate a fusion, for 
we have found no cases of incipient marginal splitting in our exam- 
ination of adult shells. 
Foetus 1 shows a unilateral fusion of comparatively slight 
extent, involving only 5 scutes and confined to the right side. 
There are 57 free scutes in band 1 and 58 in band 2 (fig. 4, 1). 
Foetus 11 shows a bilateral fusion of small extent, involving 
7 scutes on the right and 4 on the left. There are 51 free scutes 
in band 1 and 49 in band 2 (fig. 4, 11). 
Foetus 11 shows an extensive unilateral fusion, involving 21 
scutes and confined to the right side. ‘There are 40 free scutes 
in band 1 and 39 in band 2 (fig. 4, m1). 
Foetus Iv shows the same condition as does foetus III except 
that there are 19 fused scutes instead of 21. There are 41 free 
scutes in each of the first two bands (fig. 4, Iv). 
The following points may be noted: 
1. The fusion in the first two bands occurs in all individuals but 
differs in its extent and in the unilaterality or bilaterality of its 
