Page:Popular Science Monthly Volume 78.djvu/540

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of Kellogg and Bell.[1] They decide against natural selection, but their evidence for the lady beetle, Hippodamia convergens, can not be regarded as conclusive since they have made no direct comparison of eliminated and surviving individuals. Their case for the honey bee where observations are made upon free flying individuals and those which have not yet left the shelter of the hive, is much better, but even here I must feel that their numbers are too small to give finally conclusive results in a problem so difficult as that of natural selection. Furthermore, they suggest that the more abnormal individuals may be made way with before they have the opportunity of leaving the hive.

A most suggestive result was obtained by Schuster in an investigation of deep and shallow water crabs of the genus Eupagurus[2] He finds that for both sexes, but especially for the males,[3] the individuals from deep water were more variable than those from shallow water.[4] Schuster wisely leaves the determination of the reason for this difference in variability to the time when more data, and data collected under the guidance of this first study, shall be available. He points out, however, that if these differences in variability are not those of deep water and shallow water local races, but arise anew in each generation, they must be due either to the direct influence of the environment or to selection. If elimination be the true explanation the less variable shallow-water forms would be regarded as a selection from the more variable deep-water population.

Turning again to studies carried out primarily to test the possible action of natural selection, we may mention the work of Browne on the medusa, Aurelia aurita[5] In this jelly fish the number of marginal sense organs, tentaculocysts, is definitely fixed in the larval stage commonly known as the Ephyra, and by a comparison of collections of Ephyæ and adults it is possible to determine whether variation in the number of the marginal sense organs affects the chance of survival from larval to adult life. Since all of the young and adult populations compared were sensibly identical, one must conclude that neither an increase nor a decrease in the number of tentaculocysts is so injurious that there is any selective elimination during development.

Crampton's study of pupal and pupal-imaginal elimination in the

  1. 12 Kellogg, V. L., and Ruby G. Bell, "Studies of Variation in Insects," Proc. Wash. Acad. Sci., Vol. VI., pp. 203-332, 81 figures, 1904.
  2. Schuster, E. H. J., "Variation in Eupagurus prideauxi," Biometrika, Vol. II., pp. 191-210, 1903.
  3. 14 Deep water forms were those taken at a depth more than 35 meters; shallow water forms from a depth of less than 35 meters.
  4. The males are more variable than the females, in both deep and shallow water.
  5. "Browne, E. T., "Variation in Aurelia aurita," Biometrika, Vol. I., pp. 90-108, 1901.