370 JOHN C. PHILLIPS 
in F,. If in such cases dominance is lacking, an apparently blend- 
ing inheritance results, attended in F; by no increase of varia- 
~ bility, but in F, by greatly increased variability. 
Now this, as Emerson has shown, is exactly what happens in 
size inheritance in plants. Such eases are therefore open to in- 
terpretation as Mendelian inheritance without dominance, in 
which more than a single unit character is involved. The theo- 
retical aspects of the matter have been fully discussed by Lang 
(10) and Castle (11). 
The following preliminary results (summarized in table 1) from 
a cross between two different size races of ducks show indications 
of segregation in body weight. As it will be some time before 
further data can be added, it is thought worth while to record the 
experiment as far as 1t has progressed. 
An experiment of this sort, based, as it must be, on the perfect 
health of the animals, is necessarily subject to a serious source of 
error. Larger numbers than have yet been obtained are there- 
fore desirable, and it is hoped that these may be had in future 
seasons. The season of 1911 was very dry and hot and may have 
had some effect on the variability of the F, generation. It was 
certainly not favorable toward fertility in duck eggs. The Fi 
generation is much too small and an attempt will be made to 
obtain larger numbers, using as mothers random females from the 
small race. Tarsus and bill measurements will also be taken to 
supplement the weights of the animals. 
MATERIAL 
Ducks were chosen for this purpose because it is possible among 
them to obtain two races greatly different in size, and yet produc- 
ing fertile hybrids. Important also is the fact that the young can 
be raised in large numbers during a single definite growth season. 
Maturity is reached quickly, and entire lots can be killed and ex- 
amined at the same age. It is possible also to raise different 
groups or generations during the same season, thus providing a 
check upon environmental effects. 
The large French Rouen duck was chosen for the large parent 
and the common domestic mallard for the small parent. 
