for, as I understand, both female forms occur on the same island. I quite agree with your distinction between dimorphic forms and varieties; but I doubt whether your criterion of dimorphic forms not producing intermediate offspring will suffice, for I know of a good many varieties which must be so called that will not blend or intermix, but produce offspring quite like either parent.英文原著 · 《More Letters of Charles Darwin Volume I》
My belief certainly is that number of offspring is not so important an element in keeping up population of a species as supply of food and other favourable conditions; because the numbers of a species constantly vary greatly in different parts of its own area, whereas the average number of offspring is not a very variable element.英文原著 · 《More Letters of Charles Darwin Volume I》
By proving that the offspring of cross-fertilisation are more vigorous than the offspring of self-fertilisation, he showed that one circumstance which influences the fate of young plants in the struggle for life is the degree to which their parents are fitted for cross-fertilisation. He thus convinced himself that the intensity of the struggle (which he had elsewhere shown to exist among young plants) is a measure of the strength of a selective agency perpetually sifting out every modification in the structure of flowers which can effect its capabilities for cross- fertilisation.英文原著 · 《The Life and Letters-2》
"Cross-fertilization," says Darwin, "results in offspring which vanquish the offspring of self-fertilization in the struggle for existence." This has been the motto of the orchid family for ages. No group of plants has taken more elaborate precautions against self-pollination or developed more elaborate and ingenious mechanism to compel insects to transfer their pollen than this.英文原著 · 《WILD FLOWERS》
It was inevitable that before the sons of women such as these, the sons of the parasitic Roman should be swept from existence, as the offspring of the caged canary would fall in conflict with the offspring of the free.英文原著 · 《Woman and Labour》
"'Tis ill treatment for a gentleman who wants an heir," the old woman answered, as disrespectful of his spouse as he was, being a time-serving crone, and knowing that it paid but poorly to coddle women who did not as their husbands would have them in the way of offspring. "It should have been a fine boy, but it is not, and my lady--"英文原著 · 《A Lady of Quality》
What if evolutionarily they're programmed to hold onto the past in order to educate their offspring about the perils of going out-- Jesus!美剧 · 《Shameless》
And you owe it to yourself and to posterity to protect The genetic integrity of your sister's future offspring.美剧 · 《The Big Bang Theory》