Abstract
The tail of a mouse is characterized by scales which are arranged in more or less regular rings. Taxonomists long ago recognized the systematic value of the average number of tailrings. For Mus musculus this is given at about 180.
In 400 albino mice obtained from the animal house of the Peking Union Medical College—all of them descendants of 32 animals imported from the Rockefeller Institute, Princeton, N. J., by Dr. C. TenBroeck in 1924—the number of tailrings, counted after the death of the animal, varied from 142 to 220, with an average of 189.38±0.62. (The standard deviation is ±12.57.) On account of the irregularity of some rings, the number of tailrings of a given mouse cannot be stated with absolute accuracy; it may be 2 more or less than the number actually counted. The correlation of the number of tailrings with the length of the tail is low. (The coefficient of correlation is 0.27±0.05.) In general, therefore, fewer rings mean broader rings.
Selection of the number of tailrings in these mice was tried simultaneously in the direction of high and of low number and all animals were kept in the same room and treated in the same way. This prevents crediting any changes in the number of tailrings to changes in the environment.
Selection was based on the number of tailrings counted in the living mouse. For the low number of tailrings (series L T M) 4 mice were chosen which appeared after death to have 152, 154, 178, and 196 tailrings. Of course, the selection of the last one for this group was a mistake. After 7 months these 4 mice had altogether 65 descendants. In 58 of them the tailrings were counted after death.
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