GAMETIC COUPLING AND REPULSION IN THE SILKWORM. 
143 
upon the results of several matings from the various lots. On the whole these 
experimental results set forth in the preceding pages are, as far as they go, 
almost exactly what we should expect to get if our assumption is correct. 
Furthermore, though the numbers of the individuals reared were not 
sufficiently large to determine the gametic series, I am inclined to think 
that the partial coupling in my case was on the 7 : 1 : 1 : 7 system. The 
actual figures are in fair accordance with the theoretical expectation on that 
system. 
As may be seen from what I have given in the historical review, partial 
repulsion is less common than partial coupling. In plants the examples of 
repulsion as yet known are for the most part perfect, while the majority of 
coupling phenomena is partial. The same rule probably also holds good with 
animals. At least with the Silkworm such seems to be the case, for I have 
encountered here two examples of partial and one of complete coupling, 
while the three cases of the repulsion were all complete. 
A striking fact has been found with regard to the genetic interrelation 
of the striped marking and yellow colour. It is the occurrence of two 
different systems of gametic coupling between these characters, a partial 
coupling on the 7 : 1 : 1 : 7 system on the one hand, and a complete 
coupling on the other. Bateson met with a similar case in the sweet pea, 
where as a result of the partial coupling of the purple colour ( i . e. the blue 
factor) with the long pollen, he obtained the 7 : 1 series in F 2 of the cross 
Blanche Burpee x Emily Henderson , while the F 3 offspring of the same 
cross showed a closer agreement with the expectation on the 15 : 1 basis. 
The latter system also appeared in F 2 of the Bush x Cupid cross. The 
question how such phenomena arise is not solved as yet. 
As to the adoption of the terms ‘coupling’ and ‘repulsion’, though their 
appropriateness may be questioned, yet I prefer from the following reasons 
to preserve them in their original sense: 1) the terms are already widely 
accepted, 2) to keep the ‘coupling’ distinguished from ‘repulsion’ is at least 
convenient, because the F 2 phenotypic ratios resulting from them are funda- 
mentally different. The term ‘reduplicated system’ may be conveniently 
used as a general name including both coupling and repulsion. 
