PHENOTYPICAL VARIATION IN BODY AND CELL SIZE OF DROSOPHILA MELANOGASTER

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Abstract
Dob-zhansky''s method of determining the number of cells under the surface of the wing membrane of D. melanogaster by counting the number of hairs has been used in the present investigation of the relationship of the organ size to the size of its cells. Underfeeding and development at low temperature have been the factors to produce flies under and above the normal size. The functional relation between the time of feeding of larvae and the size of the wings of larvae being the expression of the upper part of the logistic larval growth of the 3rd larval instar, can be expressed by a cubic parabola. There is a definite tendency for large larvae (i.e., fast-growing ones) to pupate earlier, which finds a certain analogy with Pearl''s correlation that "between growth rate and duration of life (in this case, duration of larval life) to the beginning of death the correlation is negative and significant in degree." As far as all 3 groups of flies (underfed, normal, and cold flies) are concerned, the size of the wings is negatively correlated with the number of hairs on a definite surface of the wing when the groups are considered as wholes (inter-group correlation). The existence of such a negative correlation could be shown also within the group of underfed [female] [female] and [male] [male], but not within the other groups. Expressing in % the increase in size of the whole organ and the increase of the linear dimensions of the cells there is a discrepancy in the rate of changes. This leads to the conclusion that the changes in size of the wing can not be accounted solely by the changes in the size of the cells. The number of cells must play also a certain role in this process.