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The occurrence of new characters, or mutations as they are called, has been specially studied by other investigators, and I propose briefly to consider the two most important examples of such research, namely, that by Professor T. H. Morgan, which deals with the American fruit-fly Drosophla, and the other which concerns the mutations of the genus of plants OEnothera, exemplified by our well-known Evening Primrose.
Gaudy insects, intoxicated and sensuous, have feasted and flirted throughout the hours of daylight, and certain prim moths, sonorous of flight, find subtly scented blossoms keeping open house for them the livelong night. Let others vex their souls and mutter the oddest sorts of imprecations because the fruit-fly cradles its pampered young in the juiciest of their oranges.
On the mutation hypothesis, adaptation is purely accidental. T. H. Morgan considers that the appearance of two slightly different shades of eye colour in male and female in a culture of a fruit-fly in a bottle is sufficient to settle the whole problem of sexual dimorphism, and to supersede Darwin's complicated theory of sexual selection.
The sex is thus determined by the male gamete, the X chromosome united with that of the female gamete producing female individuals, while the Y united with X produces male individuals. Professor T. H. Morgan has made numerous observations and experiments on a single culture of the fruit-fly, Drosophila ampelophila, bred in bottles in the laboratory for five or six years.
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