912 H. H. NEWMAN AND J. THOMAS PATTERSON 
variational potential of the fertilized egg. We assume that if 
the egg which produces a given set of quadruplets could be made 
to produce just one individual, this individual would have a 
potential range of variability equal to that exhibited by the set 
of quadruplets. Whether or not this assumption is justified 
depends to some extent on whether our ideas about the operations 
of the mechanism of hereditary control are sound. If one attrib- 
ute the differences between the foetuses to the fact of the unequal 
distribution of the hereditary materials, he would seem to be 
forced to the conviction that, were a single foetus to develop, there 
would be no chance for the operation of such a factor, and hence 
the heredity would be settled at the time of fertilization. This 
conclusion does not appear to be so necessary when we consider 
that, even where the egg produces only one individual, it must 
still divide into two, four, etc., blastomeres, and that each division 
affords an opportunity for an unequal distribution of hereditary 
materials. In the first cleavage, instead of producing two dis- 
tinct individuals, the egg divides its material into two bilateral 
halves, which are destined to produce the right and left sides of 
the definitive body. Now it has been shown in another connec- 
tion that the correlation between the antimetrically paired organs 
of the same individual is of the same grade as that shown to exist 
between the quadruplets. This fact simply confirms the idea 
that the variability of the sets of foetuses gives a reliable measure 
of the variational possibilities of the fertilized egg. Specific 
polyembryony doubtless furnishes a special case of intra-indi- 
vidual variability, in which the original individual breaks up into 
several strictly homologous and independent parts. 
We have realized from the beginning of our work on this subject 
that the results obtained might appear to some biologists to be 
explicable on the basis of similar or different environmental influ- 
ences operating during gestation. For these reasons we have 
been careful to select for study structures little if at all likely 
to be influenced by environmental factors. It will doubtless 
be claimed by some that the foetuses are almost identical because 
they have developed under almost identical conditions, and that 
the slight differences are the result of equally slight differences in 
