Abstract
In the egg of the silkworm fertilization under the room emperature generally takes place within approximately 2 hours after insemination. Present experiments are concerned with the tolerance of the fertilizing activity of the sperm within the egg to low temperatures applied at different times prior to the establishment of fertilization.
It was learned that the fertilizing activity of the sperm within the egg was wholly impaired by refrigeration at 2.5°C. for over 5 days, but normal fertilization took place under the temperature of 5°C. Accordingly, it appears likely that a critical point might exist within the range between 2.5°C. and 5°C. with respect to the temperature effect upon fertilization. It was of most interest to see, as the result of the cooling experiment on the eggs inseminated by the same strain and those laid after mating between different strains, that the fertilizing activity of the sperm in the latter eggs was less affected by low temperature.
Such observations as well as Umeya's experiments that reported in 1930 may throw light for the analysis of the “heterosis theory” which concerns the problem why the vigor of the silkworm is intensified by hybridization. A work is now under the way in connection with the significance of the present finding.
