140 W. J. MOENKHAUS 
for its origin is not believed. We have seen that the general vital- 
ity of the strain, as measured by its productiveness and its reaction 
to light and gravity, did not suffer as a result of seventeen gener- 
ations of closest inbreeding. Failing in this, it is not probable that 
its effect would show itelf in so specific a way as the sudden and 
complete sterility in certain males of the strain. The improba- 
bility is further supported by the fact that the inbreeding may be 
continued unabated if only care be exercised in the selection of 
the brothers and sisters to be mated, thereby even eliminating 
practically what sterility may have existed. 
It is much more probable that the sterility arose spontaneously 
in this strain or that it is present to a varying degree in this 
species. With the character present and highly transmissible 
and subject to selection it is only necessary to carry on indiscrim- 
inate breeding to have the character appear in varying intensi- 
ties depending upon the chance combinations. The rule of 
inbreeding would be only to intensify the chance combination of 
the character and to insure the more or less continued presence 
in the successive generations. 
That this character of sterility is not unique to this inbred 
strain is evident from its rather frequent presence in pairs not 
inbred. In my own experience this sterility nearly always showed 
itself in the males. In one instance I found among a brood, besides 
a sterile male, two females that failed to deposit eggs although 
eggs were evidently present in the oviducts. Similarly Castle 
found in his strain a considerable amount of sterility, and this 
in some cases among the females. We see, therefore, that sterility 
is not altogether rare even in broods that were not inbred. 
The same facts doubtless hold for the character of productive- 
ness. Castle has shown this to be transmissible and amenable 
to selection. Inbreeding does not produce it but is instrumental, 
with indiscriminate mating, in intensifying it, or, if the strain be 
not eliminated thereby, of preserving it in the strain. 
