i68 
Journal of Agricultural Research 
Vol. XXVI, No. 4 
the genetic constitution of an otocephalus, would yet be normal and 
would live and breed, while the genetic considerations lead us to believe 
that all animals in a given advanced subline of an inbred family are of 
the same or very nearly the same genetic constitution. We can assume 
in harmony with the experimental results of Dareste (2), Stockard (<?, 9), 
Lewis (j), Werber (jj), and others that the actual occurrence of an 
otocephalus or cyclopean within shch a line is due to particular environ¬ 
mental conditions. The part which genetic factors play is to determine 
differences in the susceptibility to such conditions. There is segregation 
of different degrees of susceptibility in the early generations of such a 
family as No. 13, followed by the relative fixation of a particular level 
in each subline as some combination of favorable factors becomes homo¬ 
zygous. Thus lines starting from matings 13-3-11 and 13-4-18, in 
which about 1 per cent develop into otocephali under the prevailing con¬ 
ditions, segregated from the lines starting from 13-2-7, 13-3-13, and 
13-4-9, in which none developed. 
The sudden jumps in the percentage of otocephali starting from 
I 3"' I 3~ I » I 3 _I 9~ I > and perhaps 13-16-3 can probably best be interpreted 
as mutations. The experiments of Dareste, Stockard, and others have 
shown that otocephaly or the closely related cyclopean condition is a 
defect which can be brought about by a great diversity of agents, tem¬ 
perature, low oxygen pressure, magnesium salts, butyric acid, and even 
mechanical disturbance. Apparently anything which depresses metabo¬ 
lism sufficiently at a certain critical moment in development acts most 
drastically on the sensitive anterior end of the central nervous systems, 
resulting in this type of monster. It is to be expected that the genetic 
factors which determine high or low resistance to such conditions would 
also be highly general in nature. Any factor which influences the level 
of metabolism at the critical moment should have the same effect. Thus 
mutations which influence the tendency toward otocephaly should be 
relatively numerous. Most of them should increase the tendency on the 
principle that a chance mutation is more likely to disturb normal adjust¬ 
ments than to improve them. Thus the pedigree of Family 13, with its 
1 per cent tendency starting from 13-2-5, jumping to a 4 per cent tend¬ 
ency in one subline 11 generations later, and this subline jumping to 
more than 20 per cent in a branch six generations later, is just what 
should be expected. 
The distribution in other families, such as No. 19 and 32, in which the 
otocephali occurred only in early generations, is explainable as the result 
of early segregation and chance displacement of the susceptible lines 
by resistant ones. Family 13 might have had this history if it had been 
the descendants of 13-3-13, which had multiplied most rapidly, instead 
of those of 13-4-18. 
THE RESULTS OF CROSSES 
If there are genetic differences only between different inbred lines, 
not within them, it is not an easy matter to learn much of the details of 
their inheritance. There is one point of considerable importance, 
however, on which there is some evidence. It is conceivable that 
otocephaly may be a maternal character so far as its hereditary basis is 
concerned. That which is inherited may be a tendency toward faulty 
implantation of the ovum (the factor Mall considered most important) 
or a tendency toward the production of toxic metabolic products with 
