906 H. H. NEWMAN AND J. THOMAS PATTERSON 
organic relation. How surprisingly alike are the members of the 
pair may be realized by an examination of table 6. A glance 
down the column of totals will reveal the frequency with which 
exact identity exists between the paired individuals and how rarely 
such is the case between individuals of opposite pairs. 
It might be claimed that any method of pairing would give a 
closer correlation than that derived from a treatment of the whole 
set. That this claim is without justification is readily shown by 
the experiment of pairing the foetuses in different ways and deter- 
mining their correlation constants. There are two other possible 
ways of pairing the quadruplets. We may put together the adja- 
cent members of opposite pairs, associating foetus I with Iv and 
II with 111, or we may pair them diagonally, associating 1 with 11 
and 1 withtv. The result of the experiment is shown below: 
Correlation coefficient, true pairs (I-11) and (111-1v) = 0.9517 
Correlation coefficient, false pairs (I-1v) and (11-111) = 0.9270 
Correlation coefficient, false pairs (1-111) and (11-rv) = 0.93894 
It will be noted that the correlation constants for both of the 
false pairs differ only to a slight extent from that of the whole 
set; which shows conclusively that there is no intra-fraternal 
correlation on the basis of either of these artificial groupings. 
The pairing relation is brought out even more strongly in the 
study of atypical scute and band conditions. In each set dealt 
with reference has been made to the instances of pairing as they 
occurred, and in several cases it was shown that pairing was exhib- 
ited in several different ways in the same set. No more convinc- 
ing evidence of the reality of pairing could be asked for than is 
afforded by the conditions seen in sets 64, 96 and 101. 
The fact of pairing would seem then to need no further dem- 
onstration; but its underlying causes and its relation to the 
mechanics of hereditary control are problems that require much 
consideration. 
It must be frankly admitted that so far we have failed to prove 
conclusively that each foetus in a set is the product of a single 
blastomere of the four-cell stage. The youngest embryonic 
vesicles appear to be still single individuals so far as any visible 
